. Aug 16;59(6):&#;. doi: 10./s-021--x

Effects of extrusion temperature and puffing technique on physical and functional properties of purpled third-generation snack after heat treatment

Hataichanok Kantrong

Hataichanok Kantrong

1Institute of Food Research and Product Development, Kasetsart University, P.O. Box , Kasetsart, Bangkok, Thailand Find articles by Hataichanok Kantrong 1,&#;, Supakchon Klongdee

Supakchon Klongdee

1Institute of Food Research and Product Development, Kasetsart University, P.O. Box , Kasetsart, Bangkok, Thailand Find articles by Supakchon Klongdee 1, Suveena Jantapirak

Suveena Jantapirak

1Institute of Food Research and Product Development, Kasetsart University, P.O. Box , Kasetsart, Bangkok, Thailand Find articles by Suveena Jantapirak 1, Nipat Limsangouan

Nipat Limsangouan

1Institute of Food Research and Product Development, Kasetsart University, P.O. Box , Kasetsart, Bangkok, Thailand Find articles by Nipat Limsangouan 1, Worapol Pengpinit

Worapol Pengpinit

1Institute of Food Research and Product Development, Kasetsart University, P.O. Box , Kasetsart, Bangkok, Thailand Find articles by Worapol Pengpinit 1

1Institute of Food Research and Product Development, Kasetsart University, P.O. Box , Kasetsart, Bangkok, Thailand

Revised Jun 21; Accepted Aug 9; Issue date Jun.

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© Association of Food Scientists & Technologists (India) PMCID: PMC  PMID:

Abstract

This work aimed to investigate the effects of extrusion temperature (100 105 and 110 °C) and puffing technique (microwaving (210, 420 and 560 W.) and deep frying (170 and 190 °C)) on physical and functional properties of third-generation snack containing purple sweet potato and butterfly pea flower. Snack qualities in terms of physical properties (expansion ratio, bulk density, color and texture) and functional properties (total anthocyanin content, total phenolic content and antioxidant capacity) were subsequently determined. The results showed that extrusion temperature did not significantly affect the color of snack pellets. However, it significantly affected the functional properties of the snack pellets. Snack pellet produced from extruder at 110 °C contained significantly higher functional properties when compared to those extruded at 100 and 105 °C (p&#;<&#;0.05). In addition, the study of the puffing method indicated that an increase of microwave power level and frying temperature resulted in a decrease of hardness. On the other hand, the increase of microwave power level and frying temperature caused an increase of antioxidant capacity in the puffed snacks. Moreover, microwave puffing could help preserve the color and antioxidant capacity better than deep frying. Especially, microwaved snack had total anthocyanin content twice more than that puffed by frying.

Supplementary Information

The online version contains supplementary material available at 10./s-021--x.

Keywords: Anthocyanin content, Extrusion, Frying, Microwave, Snack pellet

Introduction

Snack foods are popular products for all ages. It is a ready-to-eat food which is not a main meal but normally eaten between meals to avoid hunger or craving. Currently, the way of people&#;s life is rapidly changed into an urbanization that encourages consumers to focus on convenience store and easy way to get foods. Thus, the market demand of ready-to-eat food, instant food, and frozen food are increased.

According to the market survey, extruded snacks have high % market share when compared with another kind of snacks. The extruded snack can be divided into two generations, the first one namely second-generation or expanded snack. This kind of snack does not need any other process for puffing the product, thus extrudates launched out from the extruder are distributed to the drying and seasoning process. While, the second type of extruded snack called third-generation snack need the puffing process. The third-generation snack or &#;pellets&#; referred to as semi or half product which have hard gel-like and highly-dense appearance. This type of snack requires further process to puff such as hot oil, hot air puffing or microwaving. Recently, the third-generation snack has become of interest because it can be kept longer than the puffed snacks, it has high bulk density which is easy for packing and transporting. These snack pellets can be sold to consumers as ready-to-eat snacks or sold directly to the consumer for preparation at home (Huber ; Riaz ).

A wide range of raw materials can be selected and added to produce excellent recipes for third-generation snacks. However, consumers concern more about their health nowadays thus they eat more natural and organic foods produced from healthier sources of raw materials. Therefore, this work focused on producing healthy snack pellets by adding agricultural raw material containing anthocyanin including purple sweet potato and butterfly pea flower in order to enhance functional properties in the snacks. As we known, anthocyanins are very sensitive to heat and can be lost during food processing. Thus, aim of this study was to investigate the effect of extrusion temperature as well as the effect of puffing techniques on the physical and functional properties of the puffed products, for example expansion ratio, bulk density, texture, color, total phenolic content, antioxidant capacity and total anthocyanin content. Puffing techniques utilized in this work were traditional method namely deep frying and microwaving. The heat source in microwave is from an electromagnetic wave which interact with the water molecule in the food products so that this technique do not need cooking oil for puffing and the consumer can prepare puffed snack at home. The results from Ernoult et al. indicated that the general snacks in the market normally contain 20&#;40% fat content. Due to the healthy foods demand, low fat and low sugar snacks are continuously increasing in popularity particularly middle-aged and elderly groups who prefer eating food that does not adversely affect their health. Therefore, in order to reduce the amount of oil in snack pellets, puffing by microwave also requires further study to meet the health concern in groups who prefer eating snacks.

Bringing all of this into account, the objective of this study was to investigate the effects of extrusion temperature and puffing technique on physical and functional properties of third-generation snack from purple sweet potato and butterfly pea flower.

Materials and methods

Raw materials

Purple sweet potato powder

Purple sweet potatoes were purchased from wholesale market in Pathum Thani province, a neighboring province of Bangkok, Thailand. After that, they were thoroughly washed by tab water, peeled the skin, cut in to small pieces then steamed for 10 min and ground into the paste form. The purple potato paste was processed into dried form by drum dryer under the drying temperature of 130 °C and 3 rpm of drum speed. After that it was ground by the Fitz mill (Fitzpatrick, M5 model, USA.) with 60 mesh screen to make a powder form. Initial moisture content of purple sweet potato powder was 9%w.b.

Butterfly pea flower powder

Dried butterfly pea flowers were bought from farm in Tak province of Thailand. They were ground by using Fitz mill with 60 mesh screen. Its moisture content was found to be lower than 10% w.b.

Preparation of mixed ingredient

The purple sweet potato powder 20% and 1% of butterfly pea flower were mixed with 37% potato flake (Idaho Pacific, USA. The moisture content about 8&#;9% w.b.), 14% wheat flour (UFM, Thailand. and the moisture content was lower than 10% w.b.), 24% corn flour (Knorr, Thailand. % M.C. was 8.5%w.b.) and other ingredients (salt, sugar, Monoglyceride and baking soda) using mixer (KitchenAid, 5K5SS model, USA). The moisture content of the mixed sample was found to be 8.9% w.b.

Extrusion process

The extrusion process was carried out using an intermeshing co-rotating twin screw extruder (Hermann Berstorff Laboratory, ZE25&#;×&#;33D model, Germany) with the L/D ratio of 870:25. This extruder consisted of 7 barrel parts ending with a 24.5 mm thick die plate with 1 mm height and 2 cm length square die hole. The extruder was operated at 3 levels of barrel temperature No.5 which was the highest barrel temperature (100, 105 and 110 °C) and the temperature in each barrel was set according to the following temperature profiles as shown in Fig. 1. A screw of the extruder was operated at the speed of 200 rpm, the mass flow rate of the mixed ingredient was averaged at 5.8 kg/hr and the feed moisture was controlled at 19% w.b. After the extrusion process, extrudates were dried at 40 °C for 4 h. until the final moisture content was lower than 10% w.b. after which they were kept in aluminum foil bag before further experiment.

Puffing process

There were two methods used in this study for puffing the snack pellets which included deep frying and microwave puffing.

Deep frying condition

Before frying, palm oil was preheated to the desired temperature of 170 and 190 °C for 15 min. Ten pieces of snack pellets were placed in a mesh colander and fried with preheated palm oil. The frying time of snack pellets at 170 and 190 °C were 10 and 8 secs, respectively. The ratio of snack pellet to oil used was 10 pieces per 300 ml of palm oil. After frying, samples were placed on the blotting paper to remove the excessive oil before packed in aluminum foil bag for the quality analysis.

Microwave puffing

Ten pieces of snack pellets were puffed by heating in a domestic microwave oven (Electrolux, EMSGX model, PRC) at various microwave power level (210, 420 and 560 W). The puffing time of snack pellets at 210, 420 and 560 W were 35, 25 and 15 secs, respectively. The power of the microwave oven was calibrated using the standard procedure (IMPI 2-L test) (Buffler ). After that, they were kept and sealed in an aluminum foil bag for the further analysis.

Experimental design

As mentioned above, the extrusion temperature, microwave power level and frying temperature were selected as independent variables in this study. A full factorial experimental design was utilized to design the experiment as shown in Table 1. The effects of extrusion temperature, microwave power level and frying temperature were considered by an analysis of variance (ANOVA) and Duncan&#;s multiple range tests was used to compare the mean values at a confidence level of 95%.

Table 1.

Treatment The maximum barrel temperature (barrel No.5) (°C) Puffing technique Microwave power
(W) Frying temperature (°C) 1 100 560 &#; 2 100 420 &#; 3 100 210 &#; 4 105 560 &#; 5 105 420 &#; 6 105 210 &#; 7 110 560 &#; 8 110 420 &#; 9 110 210 &#; 10 100 &#; 170 11 100 &#; 190 12 105 &#; 170 13 105 &#; 190 14 110 &#; 170 15 110 &#; 190

Physical and functional properties evaluation of puffed products

Physical qualities evaluation

Expansion ratio and bulk density

Expansion ratio was calculated as the average area of the puffed product divided by the area of the die hole. A Vernier caliper was used to measure the height and length of the puffed extrudate and a die hole. In addition, the bulk density of puffed snack was determined by dividing the mass of the product (g) by volume (ml).

Textural properties

Hardness and crispness of puffed snack were analyzed using Texture Analyzer (Stable Micro System, TA-XT2i model, England) with 5 kg. load cell. Warner&#;Bratzler: HDP/BSW probe was used to measure textural properties of the snacks. Ten samples of puffed snack were punctured by the probe at pre-test speed of 1.0 mm/s, test speed of 2.0 mm/s, post-test speed of 10 mm/s, distance 15 mm and trigger force of 10 g. The results of hardness were obtained from the maximum peak force of the curve and crispness was determined by the number of major positive peaks obtained in the product during compression (Chakraborty et al. ). Reported results were the mean ± standard deviation.

Color measurement

To measure the color of puffed products, samples were ground into powder before analysis. The color was measured in CIE color system using calorimeter (HunterLab, ColorQuest XE model, Reston, VA). The color of the sample expressed as L* a* and b*, where L* represents lightness, a* represents redness and b* represents yellowness. Calorimeter used was calibrated by using a standard white tile prior to each measurement.

Functional properties characteristic

Determination of total anthocyanin content

Five grams of sample was ground into powder and extracted with ethanol-1.5 N hydrochloric acid (85:15), then filtered using filter paper (Whatman No.1). A 2 ml of filtered clear solution was then diluted with extracting solvent to 100 ml. The absorbance was measured using spectrophotometer (Thermo Fisher Scientific, Genesys 10uv-vis model, USA) at 535 nm. The total anthocyanin content was calculated according to the following equation.

TACY=O.D.×DV×100×TEV×1SV×SW×E

where TACY is Total anthocyanin content; mg/100 g sample, O.D. is Optical density of diluted extract, DV is Volume of diluted extract (ml), TEV is Total volume of extraction (ml), SV is Volume of extracted solution (ml), SW is Weight of sample (g), E is Extinction coefficient of Cranberries (98.2).

Sample extraction for antioxidant capacity and total phenolic content analysis

One gram of sample powder in a conical tube (50 mL) was extracted with 10 ml. of 80% methanol in an ultrasonic cleaner (GT sonic, QTS model, China) for 15 min and centrifuged at  rpm for 10 min with a centrifuge (Thermo Fisher Scientific, Legend X1R model, Germany). The extraction was repeated for 3 times and the supernatants were pooled. Finally, the supernatants were diluted with the extraction solvent and brought up to 50 mL for further analysis.

Determination of antioxidant capacity

An antioxidant activity of snack pellet and puffed snack were analyzed by using the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay based on the method described by Sensoy et al. (). DPPH radical scavenging ability presents the ability of the food product to resist oxidation. Extracted sample (1 ml) was mixed with 1 ml of DPPH solution at the concentration of 200 μM. Then mixed solution was vortexed immediately and incubated in the dark place at room temperature for 30 min. After incubation, the absorbance of all samples was measured at 515 nm in 1 ml cuvettes using spectrophotometer.

Working standard solutions were prepared by diluted Trolox solution at the concentration ranging from 0 to 100 μM. All standard solutions were treated similar to those of extracted snack sample prior to absorbance measurement at the wavelength of 515 nm.

Determination of total phenolic content

Total phenolic content of snack samples were determined by using Folin-Ciocalteu reagent assay described by Li et al. () with slight modification. Gallic acid was used as a standard and the gallic acid solution (100 mg/l) was diluted with distilled water to make an appropriate concentration for the standard curve. To analyze the TPC content, 0.2 ml of extracted sample or gallic acid standard was diluted with 2.6 ml and then mixed with 0.2 ml of Folin-Ciocalteu reagent. The mixed solution was vortexed immediately and incubated at room temperature for 6 min. After that, 2 ml of 7% Na2CO3 was added, vortexed and incubated at room temperature for 90 min. After incubation, the absorbance of all samples was measured at 750 nm in 1 ml cuvettes using spectrophotometer.

Stock solution of gallic acid at  mg/L was prepared in the deionized water. Working standard solutions were prepared by diluting the stock solution to make a final concentration of 100, 80, 60, 40, 20 and 0 mg/L in deionized water. All standard solutions were treated similarly as those of extracted snack sample prior to absorbance measurement at the wavelength of 750 nm.

Sensory evaluation

The sensory attributes in terms of appearance, color, flavor, texture and overall acceptability of puffed snacks were evaluated by forty untrained panelists. The hedonic preference test was used on a scale of 1&#;9 where 1&#;=&#;dislike extremely; 5&#;=&#;neither like nor dislike and 9&#;=&#;like extremely. The snack pellets extruded at 105 °C were selected to puff by microwave puffing at 560 W and frying at 170 °C for the sensory evaluation. The results were expressed as the mean value.

Results and discussion

Snack pellets

As mention before, the snack pellets were produced by an extruder at different extrusion temperature (100, 105 and 110 °C). Qualities of the snack pellets were compared and the results are shown in Table 2.

Table 2.

Extrusion temperature (°C) Moisture content
(% w.b.) Qualities of snack pellets L* a* b* Total anthocyanin content (mg/100 g dry mass) Total phenolic content (mg GAE/ 100 g dry mass) Antioxidant capacity (mmol Trolox / 100 g dry mass) 100 9.66&#;±&#;0.07 44.72&#;±&#;1.36a &#;5.85&#;±&#;0.90a 1.87&#;±&#;0.57a 1.327&#;±&#;0.012a 6.3&#;±&#;1.8a 38.5&#;±&#;6.3a 105 9.56&#;±&#;0.08 47.69&#;±&#;2.62a &#;6.03&#;±&#;0.36a 1.67&#;±&#;0.11a 1.291&#;±&#;0.113a 5.9&#;±&#;1.3a 47.2&#;±&#;4.6a 110 9.47&#;±&#;0.18 47.26&#;±&#;0.01a &#;6.04&#;±&#;0.00a 1.92&#;±&#;0.01a 1.590&#;±&#;0.007b 10.8&#;±&#;1.4b 120.5&#;±&#;11.0b

The color results indicated that extrusion temperature did not affect the color of the snack pellet. On the other hand, it affected the functional properties of snack pellets. The results in Table 2 showed that snack pellet produced from extruder at 110 °C contained significantly higher total anthocyanin content, total phenolic content and antioxidant capacity when compared to those extruded at 100 and 105 °C. This might be due to a higher extrusion temperature could increase the amount of biologically important monomer and dimers, providing that food matrix is disrupted at high temperature (Brennan et al. ). In addition, an increase of extrusion temperature could partially break down the ester bonds between phenolics and cell walls or components of complex structures. Similar increases were reported in the work of Hu et al. (), Reyes et al. () and Saltveit ().

Puffed third-generation snack

Physical properties

The results of snacks after puffing using different puffing methods are shown in Table 3.

Table 3.

Extrusion temperature (°C) Microwave power level Frying temperature (°C) Final moisture content
(% w.b.) Expansion ratio Crispness Total phenolic content (mg GAE/100 g dry mass) Antioxidant capacity (mmol Trolox / 100 g dry mass) 100 210 0 4.90&#;±&#;0.03 2.68&#;±&#;0.14abc,A 5.2&#;±&#;1.8a,A 390&#;±&#;13gh,A 29&#;±&#;2bc,A 100 420 0 4.71&#;±&#;0.07 2.66&#;±&#;0.08abc,A 6.0&#;±&#;1.9a,A 369&#;±&#;28 fg,A 27&#;±&#;2b,A 100 560 0 4.53&#;±&#;0.01 2.76&#;±&#;0.12c,A 5.4&#;±&#;2.7a,A 341&#;±&#;28cde,A 37&#;±&#;2 h,A 100 0 170 3.86&#;±&#;0.00 2.52&#;±&#;0.22a,A 5.2&#;±&#;2.3a,A 352&#;±&#;30def,A 26&#;±&#;2b,A 100 0 190 2.72&#;±&#;0.03 2.58&#;±&#;0.22ab,A 7.0&#;±&#;1.5a,A 451&#;±&#;23j,A 33&#;±&#;2ef,A 105 210 0 4.75&#;±&#;0.03 2.62&#;±&#;0.13abc,A 5.6&#;±&#;3.2a,A 334&#;±&#;10 cd,A 31&#;±&#;1d,A 105 420 0 4.45&#;±&#;0.02 2.68&#;±&#;0.10abc,A 5.6&#;±&#;2.1a,A 374&#;±&#;25 fg,A 35&#;±&#;2fgh,A 105 560 0 4.08&#;±&#;0.01 2.71&#;±&#;0.13bc,A 5.2&#;±&#;2.8a,A 372&#;±&#;24 fg,A 36&#;±&#;3gh,A 105 0 170 2.85&#;±&#;0.07 2.56&#;±&#;0.18ab,A 7.2&#;±&#;1.5a,A 360&#;±&#;25ef,A 26&#;±&#;2b,A 105 0 190 2.65&#;±&#;0.03 2.57&#;±&#;0.17ab,A 6.0&#;±&#;2.7a,A 428&#;±&#;25i,A 34&#;±&#;1 fg,A 110 210 0 4.96&#;±&#;0.08 2.72&#;±&#;0.12bc,A 4.2&#;±&#;1.9a,A 309&#;±&#;25ab,B 30&#;±&#;3 cd,A 110 420 0 4.54&#;±&#;0.02 2.76&#;±&#;0.13c,A 5.2&#;±&#;2.2a,A 325&#;±&#;36bc,B 32&#;±&#;3de,A 110 560 0 4.24&#;±&#;0.06 2.78&#;±&#;0.12c,A 7.0&#;±&#;1.6a,A 368&#;±&#;16 fg,B 36&#;±&#;3gh,A 110 0 170 2.58&#;±&#;0.00 2.53&#;±&#;0.23a,A 5.8&#;±&#;1.5a,A 297&#;±&#;19a,B 22&#;±&#;2a,A 110 0 190 3.97&#;±&#;0.03 2.68&#;±&#;0.17abc,A 5.0&#;±&#;2.5a,A 412&#;±&#;20hi,B 36&#;±&#;2fgh,A

Expansion ratio

The results in Table 3 indicated that extrusion temperature and puffing technique were not significantly affected to the expansion ratio. However, snacks puffed by deep frying tended to less expand than microwave puffing. Moreover, the higher microwave power and frying temperature resulted in a higher expansion ratio as demonstrated by the average results of expansion ratio. In addition, the microstructure of snack pellets (extruded at 110 °C) puffed by different puffing methods were analyzed by Light Microscope (Olympus, BX511F model, Japan) as shown in Fig. 2. It was also observed that the microwaved samples were displaying numbers of air cells with larger size compared to fried samples and the higher microwave power and higher frying temperature tended to have bigger air cell size; thus, led to the more expansion.

Bulk density

Several studies have reported the important factors affecting the physical properties of snack pellets in terms of expansion ratio, shape and bulk density which are the degree of gelatinization of starch and moisture content of the pellets. The higher extrusion temperature in the range of 90&#;110 °C resulted in a higher degree of starch gelatinization. This might thus contribute to the easier formation of air cells by increasing the steam pressure during microwave puffing without rupture of its cellular structure (Lee et al. ; Camacho-Hernández et al. ). When the higher air cell was created, the expansion ratio of the puffed snack was also increased but the bulk density was decreased. However, operation the extruder at 120 °C or higher causes the damage of starch granule resulting in a decrease of viscosity in the system and decrease the degree of gelatinization which leads to the decreasing of expansion ratio (Camacho-Hernández et al. ). This study was thus conducted at the extrusion temperature in the range of 100&#;110 °C.

Statistical analysis revealed that extrusion temperature at 100 °C resulted in higher bulk density of puffed snacks than those extruded at 105 and 110 °C significantly. This might be because of a lower degree of gelatinization of the pellet extruded at 100 °C when compared to those processed at 105 and 110 °C. Therefore, it might be difficult to create the air cells inside the puffed product which perhaps led to the low expansion and thus, high bulk density were obtained. Figure 3 clearly showed that puffing the pellets extruded at 100 °C by both microwaving and frying at low level (microwave power of 210 W and frying temperature at 170 °C) caused higher bulk density of puffed snack than other puffing conditions. Notably, higher bulk density generally results in higher hardness of the snack products.

Textural properties

Textural properties in terms of hardness and crispness were presented in Fig. 3 and Table 3, respectively. Hardness of puffed snack tended to decrease when extrusion temperature, microwave power and frying temperature were increased as shown in Fig. 3. This could be because puffing at high temperature causes an increased vapor pressure in the material which resulted in more creation of air cells in the snack structure (Raikham and Rewthong ), leading to the decrease of hardness of the puffed products. In agreement with previous findings of Tovar-Jímenez et al. (), water evaporation in the products caused by microwave puffing had created the pressure difference, thus leading to the expansion of the products and generation of air cells with smooth surface and small size.

Statistical results showed that extrusion temperature significantly affected the hardness of the third-generation snack after puffing. The puffed snack extruded at 100 °C had higher hardness than that extruded at 105 and 110 °C since the higher extrusion temperature had caused the reduction of extrudate&#;s viscosity, thus forming the air cells. Combination of an increased expansion with reduced bulk density might result in the reduced hardness of the products, consistent with previous findings of Tovar-Jímenez et al. (). However, the extrusion temperature, puffing methods and puffing conditions did not significantly affect the crispness of the products as shown in Table 3.

Color

The results in Fig. 3 and statistical analysis showed that extrusion temperature did not significantly affect the lightness of the puffed snack. However, puffing technique significantly modified the color. When considering on the lightness (L*), the results showed that L* of snack puffed by microwave was not significantly different among the microwave power, while the L* value of fried snack tended to be decreased when the higher temperature was applied as shown in Fig. 3. It is possible that higher frying temperature causes the browning reaction from sugar in the raw materials as described by Truong et al. () and Mohammadi Moghaddam et al. ().

The results of redness (a*) are presented in Fig. 3, showing that the redness of fried snacks were higher than those puffed by microwave. The higher microwave power and frying temperature led to the increase of redness of the puffed snacks because of the non-enzymatic browning reaction (Nsabimana et al. ).

Functional properties

Besides the physical characteristic of puffed snacks, functional properties in terms of total phenolic content, antioxidant capacity and total anthocyanin content were also analyzed. The results were summarized in Table. 3 and Fig. 3.

Total phenolic content

Statistical analysis in Table. 3 showed that extrusion temperature significantly affected total phenolic content of puffed snack. It tended to be decreased when the higher extrusion temperature was used. The puffed snacks extruded at 110 °C had significantly lower total phenolic content than those extruded at 100 and 105 °C. This might be because high extrusion temperature damages the phenolic compounds. The increasing effect of extrusion temperature on total phenolic content was also found for the extrusion of banana flour (Sarawong et al. ) and the extruded snacks enhanced with vegetables (Bisharat et al. ).

Moreover, snack pellets fried at 190 °C had a higher total phenolic content than those fried at 170 °C and puffed by microwave. This can be explained by the fact that frying at 190 °C may have attributed to the extractability and bioavailability from the vegetables (Nur Arina and Azrina ). In addition, Ghazzawi and Al-Ismail () who studied the effects of roasting and frying of bean on an antioxidant capacity found that roasting and frying can caused the Maillard reaction which results in formation of Maillard derivatives such as pyrroles and furans that may react with Folin-Ciocalteu reagent. Thus, the total phenolic content of fried snacks was increased as showed in Table 3.

Antioxidant capacity

The results from Table 3 indicated that the extrusion temperature did not significantly affect an antioxidant capacity of puffed snacks. However, increasing of microwave power and frying temperature tended to increase the antioxidant capacity of puffed products. Previous report (Mir et al. ) showed that during thermal processing of foods, the dark color pigments were produced due to Maillard browning and these pigments extensively have high antioxidant activity. This results conformed to the L* values that the higher microwave power and frying temperature tended to decrease L*, while increased the antioxidant capacity. Consistent with this finding, Nsabimana et al. also reported that the increasing of frying temperature led to the increased of reactivity of antioxidant and the formation of new antioxidant compounds during thermal processing.

Total anthocyanin content

Statistical analysis showed that the extrusion temperature did not significantly affect total anthocyanin content of the puffed products, while the puffing technique affected total anthocyanin content significantly. Puffing by frying might destroy the anthocyanin content more than by microwaving. The higher frying temperature tended to reduce total anthocyanin content as well. Microwave power did not significantly affect total anthocyanin content as clearly shown in Fig. 3. It is possible that microwave puffing is a short time heating process which may not affect total anthocyanin content obviously as frying method, thereby preserving the anthocyanin content.

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Moreover, the results indicated that total anthocyanin content was significantly increased in the microwave puffed snacks when compared with the snack pellets. On the other hands, fried snacks had lower total anthocyanin content than the snack pellets. This results are in agreement well with the work of Nems et al. who studied the anthocyanin content and antioxidant capacity of snacks made of various kinds of colored potato. In addition, Liao et al. () suggested that microwaving of purple sweet potato lead to an increase of mono-acylated anthocyanins, whereas frying results in a reduction of total di-acylated anthocyanins and more anthocyanin is released from physical entrapment in other structures when the thermal treatment was applied. Therefore, the results in Fig. 3 clearly showed that fried snack had total anthocyanin content one fold lower than that puffed by microwaving. This suggested that the anthocyanins are very sensitive to high temperature and it tended to obviously decrease when the higher frying temperature was utilized.

Sensory evaluation of puffed snacks

In this part, the snack pellets extruded at 105 °C were selected to puff by microwave puffing at 560 W and frying at 170 °C for the sensory evaluation. Figure 4 showed a radar chart of sensory evaluation test of puffed snack. Five characteristics viz. appearance, color, flavor, texture and overall acceptability were considered for sensory evaluation. Each of the characters was evaluated on the basis of nine point scale from 1 to 9 (dislike extremely to like extremely). The results indicated that the texture was not significant different (p&#;>&#;0.05) between samples, while the appearance, color, flavor and overall acceptability of microwave puffed snack were higher than the fried snacks.

Conclusion

In conclusion, although the effect of extrusion temperature did not affect the color of snack pellets, it affected total phenolic content, antioxidant capacity and total anthocyanin content. Snack pellets extruded at 110 °C had a higher total phenolic content, antioxidant capacity and total anthocyanin content than those treated at other extrusion temperatures.

Analysis results of puffed snacks indicated that extrusion temperature did not affect the expansion ratio, but the bulk density. Puffed snack which extruded at 100 °C had the highest bulk density. Moreover, puffed snack extruded at 110 °C had the lowest total phenolic content when compared to those processed under the other extrusion temperatures.

Considering puffing technique, an increase of microwave power and frying temperature led to the lower hardness possibly due to more expand the puffed products. In addition, the antioxidant capacity was also increased because of the browning reaction from heat treatment. Furthermore, microwave puffing provided the better color, higher antioxidant capacity and total anthocyanin content, compared to frying method. Therefore, consumer prefer the microwave puffed than the fried one according to the sensory evaluation results.

Thus, the results in this study showed the possibility of microwave utilization for puffing the third-generation as opposed to the frying technique. This method does not only reduce the fat content but also preserve their texture, color and functional properties of the puffed snacks.

Supplementary Information

Below is the link to the electronic supplementary material.

Acknowledgements

This work was supported by Kasetsart University Research and Development Institute (KURDI). The authors are grateful to the Institute of Food Research and Product Development (IFRPD) for facilitating extrusion pilot plant, equipment and laboratory experiments. Finally, I would like to thanks Dr. Nutthapong Kantrong for assisting in the manuscript preparation.

Footnotes

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By Mike Pehanich, Plant Operations Editor

They&#;re not just for pet foods and kid snacks anymore. Today&#;s extruders have opened the door to a global array of new food products â&#;&#; including new nutrition-packed varieties.

More than two generations have passed since the birth of the twin-screw extruder. During this period, U.S. consumers have taken gradually to extruded foods. The most conspicuous examples of the technology â&#;&#; snacks like General Mills&#; Bugles â&#;&#; have enjoyed some marketplace success. But they have been, by and large, the flyweights of the food pyramid. When it comes to nutrition, we just haven&#;t taken them too seriously.

But time, circumstance and imagination have changed the reality if not the perception. Today, food makers around the world are discovering new ways of shaping, forming, squeezing and puffing foods not only for fun and flavor but to create healthful substance as well. Today&#;s extruders are producing crispy flat bread, baby food, pet food, high fiber products, candies, puffed snacks, pellet snacks, ready-to-eat breakfast cereals in puffed and flaked forms, meat analogues, pasta, cheese snacks and instant drinks and soups.

NOTE TO R&D

Starch content plays a major role in the type of product an extruder can produce. Rice, potato and tapioca expand well when fried. Rice yields a crunchy texture. With a lower starch content than the others, corn expands less. The resulting product has a harder texture and crunchier bite.

Wheat, oat, barley and other high-fiber grains also expand less. They are the central ingredients in healthful snacks and cereals. Expect a heavy and crunchy cereal with these grainy ingredients.

Where have all these variants come from? How is it that a pet- and snack-food technology has suddenly spilled nutrition into the processing stream?

An extruder works by taking a blend of raw ingredients in one end and subjecting it to high heat and pressure in a cylinder. As the mix passes through the extruder cooker, it is shaped and fully or partially cooked. It takes its final shape as it is forced through a die at the exit end.

Twin screw extruders welcome nearly all forms of foods and ingredients. They can handle a wide variety of granules and products with a wide range of moisture, fat, and carbohydrate content.

Their adaptability is well suited to a processing era that demands flexibility to control both capital and operations costs. Twin screw extruders permit precise control of process parameters and can perform multiple functions at once.

They are reliable machines that yield consistent product repeatedly. Furthermore, products vary little from lab to production line, making scale-up a relatively simple process.

Meaty imitationsExtruded protein extenders and meat analogues have sparked global interest. They offer alternative high-quality main-course protein foods from vegetable sources. Today processors can simulate nearly any type of fish, poultry or meat flesh in a highly palatable and easy-to-use form.Texturized vegetable proteins have found their way into thousands of formulations. Soy protein, always valued for its versatility, has become a preferred protein source offering an assortment of nutritional advantages.&#;Alternative protein sources are becoming critically important,&#; says Doug Baldwin, director of sales and marketing at Wenger Manufacturing Inc. (www.wenger.com), the Kansas City, Mo.-based manufacturer of extruders. &#;The food industry looks to extruders to process soy or other oil seeds into texturized protein.&#;

Texturized vegetable protein (TVP) is the preferred protein material for the majority of today&#;s meat analogues because, in the hands of an able processor, it can duplicate true meat fiber.

&#;A high-moisture meat analogue material doesn&#;t require drying,&#; says Baldwin. &#;It comes off the processing line with 70 percent moisture. You can get product that resembles a chicken breast fillet right off the extruder.&#;

Archer Daniels Midland (www.admworld.com), Decatur, Ill., commercialized its high-moisture meat analogue this past year. Marketed as Nutrisoy Next, it is available in a ready-to-use form.

&#;The previous generation of TVP, ADM&#;s texturized defatted soy flour, used a single screw extruder to yield a product with low moisture content â&#;&#; less than 35 percent,&#; explains Cheryl Borders, manager of soy foods applications for ADM. &#;Our new products range in moisture content from 50 to 80 percent, varying with preferred texture.&#;

The new generation of meat analogues offers convenience and quality advantages. Available in strips, nuggets, cubes and shreds, they can be used in hot or cold entrees and retort applications. The products are more receptive to flavors than previous generations of analogues. Though they can mimic beef or pork in flavor or texture, poultry has been the principal target.

&#;While you can add flavor to low-moisture extruded meat analogues, the product loses a lot of flavor when it leaves the extruder due to the pressure drop,&#; says Borders. &#;There&#;s less pressure drop with high-moisture product. As product exits the extruder and enters the cooling die, the temperature change increases the viscosity, which also helps in developing the desired texture.&#;

The technology for such products, including use of the cooling die, has been available for a quarter of a century. &#;But really, it&#;s not so much the improvement in twin screw extruders as much as the time becoming ripe for this type of analogue,&#; says Borders. &#;Seventy-four percent of consumers perceive soy as healthy today. Now they are accepting soy foods and looking for new options.&#;

The products are used by foodservice outlets or used by other food processors in entrée or component meals. They can be breaded and battered like their natural counterparts. They save the user the additional processing step of rehydration, unlike previous textured vegetable products. &#;The product is also fully cooked as it exits the cooling die,&#; says Borders. &#;That&#;s adds a convenience for the user.&#;

Two screws better than one

Twin-screw extruders have displaced their single screw counterparts in most food operations. Single-screw extruders have been relegated largely to animal feed manufacture in recent years, though some use in human food products continues.

Pre-conditioning the raw material mix for extruded product dates back to the s. &#;But learning how to utilize pre-conditioning has really advanced in recent years,&#; explains Baldwin.

Extruder size is generally given in terms of a length-to-diameter (LD) ratio; that is, the length of the overall barrel to the screw diameter. &#;We have been able to reduce the length of the extruder barrel and thus reduce hardware requirements,&#; says Baldwin.

&#;We also work more with thermal energy than mechanical energy,&#; Baldwin continues. That&#;s a plus with energy consumption an ongoing issue in the plant. &#;It&#;s more economical to process with thermal energy than with mechanical energy. If you can do more with steam during pre-conditioning, you can do more cooking with less horsepower.&#;

Clextral Inc. (www.clextralgroup.com), Tampa, Fla., was the first to adapt the twin-screw extrusion concept to food applications. The equipment maker&#;s emphasis today is on the modular concept, simplifying changeover and removal of screws, barrels and dies. New designs allow screw elements to slide onto splined shafts. They also are more hygienic and operate at higher speeds. These practical design improvements also have made the twin-screw extruder more welcome on the processing floor.

&#;Our twin-screw extruders today allow quick change of screws and easy cleaning capability,&#; notes Laurent Garcia, sales manager of Clextral. &#;With hydraulic opening, you can access the screws within five minutes for maintenance and quick changeover. You also get a good view of what is happening in the machine. You can see where the starch is gelatinized.&#;

Better temperature control and auto-mation capabilities not only have improved product quality and consistency, they also add to the flexibility and versatility of today&#;s machines. &#;You can adapt an extruder platform to new applications. Keep in place your main equipment and add auxiliary equipment for new products,&#; says Garcia.

Twin-screw extrusion offers an infinite range of possibilities, inviting innovation in mixtures of fillings and colors and a wide variety of tastes and textures.

&#;We were the first to develop flat crisp bread, coextruded with a sugar filling inside,&#; notes Garcia. &#;You can add chocolate, marmalade and other fruit-taste fillings.&#;

Snacks and RTE cereals may be the most conspicuous areas of extrusion application, but Garcia likes the possibilities opened in the nutrition area, particularly for low-carb products and texturized proteins.

Snack power

The extruder&#;s adaptability to such a wide range of raw materials has opened a large window of opportunity in snacks. Snack pellets have had more significant impact in the marketplace in Asia and the Mideast than they have in the U.S.

Economics explain part of their popularity. Pellet products begin with blended ingredients that emerge from a cooking extruder as a dense pellet. Their moisture content is reduced.

Shelf-stable pellets are passed to the processor, who prepares the final product by &#;puffing&#; it with hot oil, microwave heat, hot air or other method. In some markets, the final preparation is left to the consumer.

If you are looking for more details, kindly visit Extruded Snacks Machine.

Extruded snacks with reduced carbohydrate content are a no-brainer and already in the product mix. Extruded soy proteins will likely spread into more simulations of meat-based products.Frito-Lay, the snack giant from Plano, Texas, owns a gold mine in its Cheetos line of extruded snacks. The company has developed its own proprietary extrusion technology, company sources say. Latest is an extruder that produces a spiral Cheeto.The company&#;s most recent addition to the line is Baked Cheetos, a snack that qualifies as a healthier option with the package display of the PepsiCo Smart Spot, a marketing item Pepsico is adding to the packaging of all its &#;healthier&#; products.The current quality of today's meat analogues offers tremendous opportunity to spread good nutrition in good-tasting forms to developing nations. But the current generation of high-quality analogues carries a cost that may relegate the products to the realm of higher ticket value-added products for some time. Still, the promise of solving human hunger continues to make extrusion technology a potential savior as well as a profit maker.So sophisticated has extrusion technology become that its targets today are analogues nearly indistinguishable from the real McCoy.&#;We have done work on extruded cereal flakes and have seen interesting development in that area,&#; says Doug Baldwin of Wenger Manufacturing Inc., a Kansas City, Mo., manufacturer of extruders. &#;Processors are trying to develop an extruded flake to match the appearance, quality and texture of a processed flake.&#;Add that to a chicken breast not even the Colonel could tell from the original, and we have seen how far extruder technology has come.