Production of nutritious precooked foods in developing countries by low‐cost extrusion technology

High moisture extrusion cooking of meat analogs: A review of mechanisms of protein texturization

High-moisture extrusion cooking (HMEC) is an efficient method for converting proteins and polysaccharides into fibrous structure that is used in the industrial production of meat analogs. The purpose of this review is to systematically evaluate current knowledge regarding the modification of protein structure including denaturation and reassembly upon extrusion processing and to correlate this understanding to the structure of the final products. Although there is no consensus on the relative importance of a certain type of bond on extrudates' structure, literature suggests that, regardless of moisture level, these linkages and interactions give rise to distinctive hierarchical order. Both noncovalent and disulfide bonds contribute to the extrudates' fibrous structure. At high water levels, hydrogen and disulfide bonds play a dominant role in extrudates' texture. The process parameters including cooking temperature, screw speed, and moisture content have significant albeit different levels of impact on the texturization process. Their correlation with the ingredients' physiochemical properties provides a greater insight into the process-structure-function relationship of meat analogs. The tendency of protein and polysaccharide blends to phase separate rather than produce a homogeneous mix is a particularly important aspect that leads to the formation of fibrous layers when extruded. This review shows that systematic studies are required to measure and explain synergistic and competitive interactions between proteins and other ingredients such as carbohydrates with a focus on their incompatibility. The wide range of plant protein source can be utilized in the HMEC process to produce texturized products, including meat analogs.

Extrusion and nixtamalization conditions influence the magnitude of change in the nutrients and bioactive components of cereals and legumes

Cereal and legume diets make up the bulk of caloric sources for a majority of households in the developing world. They contain macro- and micronutrients as well as phytochemicals embedded as one matrix. Some phytochemicals are antinutritional factors which can bind nutrients thereby hindering their bioavailability. While there are other methods that can be used to enhance nutrient utilization from such foods, we summarize how food processing methods such as extrusion and nixtamalization are employed to break the food matrix and release these nutrients. Both extrusion and nixtamalization can break down complex carbohydrates into simpler, more soluble forms while at the same time inactivating or denaturing protein inhibitors and other antinutritional factors. Such disruptions of complexes within the food matrix are essential for harnessing optimum nutritional and health benefit from these foods. We present mechanistic approaches explaining how these processes enhance nutrient and mineral bioavailability and phytochemical bioactivity while minimizing the undesirable effects of antinutritional factors that coexist in the complex food matrix.

Effects of extrusion of rice bran on performance and phosphorous bioavailability in broiler chickens

BACKGROUND

Rice bran is a by-product of the rice-milling process, which remains largely underutilized; however, efficient processing treatments may improve its feeding value for chickens. This is of great economic and environmental importance, as this can lower the production costs, and offer an opportunity for valorization of a low-quality agricultural by-product, to a high-value feed source.

METHODS

This experiment was conducted to study the effect of extruded rice bran on performance and phosphorous (P) bioavailability in broiler chickens. In a completely randomized design, 200 seven-day-old broilers (Cobb 500) were allotted to five treatments with five replicates per treatment and 8 chicks per replicate, and fed with their respective diet during the starter (8 to 21 days) and grower (22 to 42 days) periods. Diets were a basal corn-soybean based diet (T1), or diets containing 20 % rice bran (T2), 30 % rice bran (T3), 20 % extruded rice bran (T4), or 30 % extruded rice bran (T5).

RESULTS

Birds feeding on T4 and T5 diets had a higher body weight gain and lower feed-to-gain ratio compared to those feeding on T2 and T3 diets (p < 0.05). Birds receiving diets containing extruded rice bran had higher total P availability and tibia ash content, as compared with those receiving diets containing un-extruded rice bran (p < 0.05). Relative weight of the pancreas was higher in birds receiving T2 and T3 diets.

CONCLUSIONS

The results confirmed the beneficial effect of extrusion treatment of rice bran on performance and P availability in broilers. Up to 30 % extruded rice bran may be included in the broiler diet without apparent adverse effects on the performance.

Development and standardization of sorghum pasta using extrusion technology

Extrusion cooking is a unique method for preparing pasta, which is generally produced from durum wheat semolina. However, preparation of pasta from sorghum is not practiced in India. Therefore, the present study was undertaken to develop and standardize pasta from sorghum cultivar, M35-1 and wheat semolina of 0.1 mm particle size. Sorghum and wheat semolina in different proportions (T1;S:W-50:50,T2;S:W-60:40,T3;S:W-70:30,T4; S:W-80:20, T5; S -100) were mixed with lukewarm water (40 °C) in the cold extruder for 30 min and passed through the extruder with a screw speed of 80 rpm and at a temperature of 55° to obtain pasta of diameter (0.6 mm) and length (1.4 mm). The extruded pasta was dried at 70 °C in a tray drier for 8 h, cooled and stored in polyethylene bags at room temperature. The pasta was subjected to physico-chemical analysis such as length, diameter, bulk density, water absorption, cooking time, cooking loss, moisture, water activity, alcoholic acidity, amylase, carbohydrates, fat, protein, fibre and ash using standard methods. Organoleptic characteristics such as color and appearance, texture, taste, flavor and overall acceptability, stickiness, bulkiness and firmness were evaluated at laboratory level by a panel of semi trained judges using 5 point hedonic rating scale. Among the various blends studied, the sorghum and wheat semolina with a combination of 50:50 (T1) and 60:40 (T2) and 70:30 (T3) were more acceptable than others. Well acceptable sorghum pasta can be developed from sorghum and wheat, thereby improving its nutritional composition.

Rheological and nutritional quality of selected dehulled legumes blended rice extrudates

Rheological and nutritional quality of ready-to-eat rice (Oryza sativa ) -legume viz. black gram (Vigna mungo), green gram (Vigna radiata), lentil (Lens culinaris) and peas (Pisum sativum) based extrudates were studied using low cost collet extruder. Extrudates were prepared keeping constant feed rate (25 kg/h) and moisture content (14% wb) at 0, 5, 10 and 15% legume incorporation levels. Rheological properties of porridge made of extrudate flour were evaluated using Rapid Visco Analyser (RVA). Maximum and minimum peak viscosity for rice extrudates alone and rice extrudates blended with 15% peas were 697 cp and 523 cp, respectively. There was a decreasing trend in degree of gelatinization with increase in legume incorporation level. Other RVA rheological parameters like trough break down and final viscosity were in the range of 266-226 cp, 431-297 cp and 452-375 cp respectively. Maximum values of protein, fat, fibre and ash contents were found in rice extrudates at 15% legumes blend levels. There was an increasing trend in nutrient contents with legume content in rice extrudates. Degree of gelatinization for rice alone extrudate was 29.4% and showed a decrease in gelatinization with increase in legumes extrudate and was minimum (22.4%) for rice blended with 15% dehulled green gram. Sensory evaluation scores for all extrudates showed the most acceptable range of 6 to 8. Thus, legume blend level (up to 15%) of dehulled legumes fetched good scores and showed promising trend for the production of low cost expanded extrudates and its instant flour.

Utilization of extrusion technology for the development of millet based complementary foods

Millet based complementary foods were developed using sorghum (Sorghum vulgare), rice (Oryza Sativa), besan (Cicer arietinum; Bengal gram dhal flour), legume mix (Green gram and roasted Bengal gram; Phaseolus aureus Roxb and Cicer arietinum) and soybean (Glycine max Merr) with a lab scale twin screw extruder. The extrudates were subjected to acceptability studies initially and at the end of the storage period i.e. 3 months at laboratory level by panel of judges using a 5-point hedonic scale. Physico-chemical characteristics like bulk density, piece density and expansion ratio were measured and proximate principles were assessed. Soy and legume mix were found to have low bulk density as well as high expansion ratio. The developed extrudates were made into fine powder and sieved through a 60 mm mesh. Malted ragi flour at 15 % level was added to the powdered extrudates to develop the complementary mixes with low bulk density. Raw formulas without malt and with malt; extruded mixes without malt and with malt were studied for viscosity. The developed mixes were made into porridge and fed to the infants and the opinions about the acceptability of mixes were collected from the mothers. The complementary mixes with malted ragi showed reduced viscosity and formed good, smooth slurry and well accepted both by children and their mothers. Extruded soy and legume mixes with addition of 15 % malt were found to have satisfactory functional characteristics and nutritive value and can be explored for bulk preparation.

Effect of the consumption of high energy dense and fortified gruels on energy and nutrient intakes of 6-10-month-old Vietnamese infants

The aim of this study was to test the ability of two new products, an instant infant flour and a food supplement containing amylases, to increase energy and micronutrient intakes of infants older than 6 months. Three groups of 48 infants were randomly constituted. Infants in groups 1 and 2 consumed at least twice a day gruel made either from the instant flour or from the food supplement. Infants from the control group received complementary foods prepared in the usual way. Each infant was surveyed during a whole day in order to measure feeding frequencies and characteristics as well as amounts of the different types of complementary foods consumed. Foods consumed by infants in the two experimental groups differed considerably in energy, micronutrient density and in consistency from the home-made complementary foods. Due to the incorporation of amylases, gruels made from the food supplement had a higher energy density, a more appropriate consistency and resulted in higher intakes per meal than gruels made from instant flour. In comparison with home-made complementary foods, both experimental products resulted in significantly higher energy and nutrient intakes. The two experimental products appeared to increase sufficiently both energy and nutrient intakes of infants to complement their breastmilk intake.

Physico-chemical characteristics, nutritional quality and shelf-life of pearl millet based extrusion cooked supplementary foods

The process variables for extrusion cooking of pearl millet were standardized and some of the physicochemical characteristics of the millet extrudates and also the nutritional qualities of the millet and legume-based extruded supplementary foods were determined. The millet grits less than 355 microm in size, equilibrated to 18+/-1% moisture content, extruded at 150+/-5 degrees C temperature and at 200+/-10 rpm of the barrel of a twin-screw extruder yielded the extrudates of 1.75+/-0.21 expansion ratio and 7.5+/-1.5 kg breaking strength. The cold and cooked paste viscosity, the melt energy and also the carbohydrate digestibility of the extrudates indicated that the products were pre-cooked and were of ready-to-eat nature. The millet was blended with grain legumes (30%) and also with defatted soy (15%) separately and extruded to prepare ready-to-eat nutritious foods suitable as food supplements to children and mothers. The foods based on the millet and legumes and also the millet and soy contained 14.7% and 16.0% protein with 2.0 and 2.1 protein efficiency ratio values, respectively. The shelf-life of the foods was about 6 months in different flexible pouches at ambient storage conditions. The study showed that applications of extrusion cooking technology to pearl millet have promise for preparation of diversified and value-added food products from the millet.

Supplementary feeding of underweight, stunted Malawian children with a ready-to-use food

OBJECTIVE

Maize and soy flour mixes are often used in the treatment of moderate malnutrition in Malawi. Their efficacy has not been formally evaluated. A recently developed ready-to-use food (RTUF) effectively promotes growth among severely malnourished children. The authors compared the effect of maize and soy flour with that of RTUF in the home treatment of moderately malnourished children.

METHODS

Sixty-one underweight, stunted children 42 to 60 months of age were recruited in rural Malawi, in southeastern Africa. They received either RTUF or maize and soy flour for 12 weeks. Both supplements provided 2 MJ (500Kcal) of energy daily but had different energy and nutrient densities. Outcome variables were weight and height gain and dietary intake.

RESULTS

Before intervention, the mean dietary intake and weight and height gain were similar in the two groups. During the supplementation phase, the consumption of staple food fell among children receiving maize and soy flour but not among those receiving RTUF. There was thus higher intake of energy, fat, iron, and zinc in the RTUF group. Both supplements resulted in modest weight gain, but the effect lasted longer after RTUF supplementation. Height gain was not affected in either group. Periodic 24-hour dietary recalls suggested that the children received only 30% and 43%, respectively, of the supplementary RTUF and maize and soy flour provided.

CONCLUSIONS

RTUF is an acceptable alternative to maize and soy flour for dietary supplementation of moderately malnourished children. Approaches aimed at increasing the consumption of supplementary food by the selected recipients are needed.

Effect of food processing on iron availability of African pearl millet weaning foods

The effects of different cereal precooking process (roasting and extrusion cooking) on iron availability and protein digestibility of four African weaning foods were investigated using in vitro methods. In two weaning foods based on pearl millet, cowpea and peanut, the cereal was extruded (A) or roasted (B). In two other weaning foods having a similar composition, a low proportion of milk powder was added and the cereal extruded (C) or roasted (D). The mean +/- SD iron values (mg/100 g) were: A, 5.56 +/- 0.18; B, 9.12 +/- 0.93; C, 5.89 +/- 0.23; D, 9.04 +/- 0.85. When the pearl millet was roasted, the iron content was higher than in the extruded weaning foods (P < 0.01). However, the percent of available iron of the roasted weaning foods was very low (B, 1.64 +/- 0.01; D, 0.91 +/- 0.02). The iron availability of the extruded weaning foods, A and C, was 3.5 times and 6.5 times higher than the corresponding roasted weaning foods, B and D, respectively. This represented 332.4 +/- 4.4 and 375.1 +/- 5.8 micrograms of available iron/100 g for A and C, respectively versus 149.5 +/- 0.9 and 82.2 +/- 1.8 micrograms of available iron/100 g for B and D, respectively. No significant differences in polyphenol contents were found according to the precooking process of the cereal. The extruded weaning foods showed a higher protein digestibility of approximately 10% than the roasted ones (P < 0.05). A positive correlation was found between in vitro iron availability and protein digestibility (r = 0.976, P < 0.02). Despite a high content of iron, the iron availability of roasted pearl millet weaning foods was quite low. Extrusion cooking of the cereal improved the protein digestibility and iron availability of pearl millet weaning foods; however, the amount of available iron remained insufficient to meet the iron requirements of infants whatever the cereal processing.

Value-added products from underutilized fish species

Fish is a rich source of easily digestible protein that also provides polyunsaturated fatty acids, vitamins, and minerals for human nutrition. Nonetheless, a large proportion of total landed fish remains unused due to inherent problems related to unattractive color, flavor, texture, small size, and high fat content. Most of these underutilized fish belong to the abundantly available pelagic species, which are landed as bycatch, and some are unconventional species such as krill. Although some species are used industrially for fish meal manufacture, a need for their conservation and utilization for human consumption has been recognized in order to prevent post-harvest fishery losses. Recovery of flesh by mechanical deboning and development of value-added products are probably the most promising approaches. This article discusses various possibilities for product development using mince from low-cost fishery resources. These include surimi and surimi-based products, sausages, fermented products, protein concentrates and hydrolysates, extruded products, and biotechnological possibilities. The dual advantages of this approach, namely, finding ways for better utilization of low-value fish species and providing protein- rich convenience foods, have been pointed out. However, the key to the success of this approach depends largely on the market strategies utilized.

Extrusion of food proteins

Protein extrusion has frustrated earlier predictions regarding its impact in the development of food products. The main reason for this disappointing performance has been its failure to yield fabricated food products with textural quality close enough to that of natural products at competitive prices. Texturized soya protein by extrusion is presently the only commercial success in this area, being incorporated into several convenience products, increasing their protein content and quality and conferring them some desirable sensory properties. Technological and scientific gaps in the extrusion texturization are still to be bridged if this technique is to be applied for upgrading unconventional protein. The precise mechanisms responsible for protein texturization through extrusion are still unclear. Proteins show a very wide range of extrusion behavior that is probably related to large differences in their association properties. New peptide bonds, formed by free amino and carboxylic groups of the protein, were postulated as being responsible for the cross-linking that takes place in protein extrusion. However, disulfide bonds and electrostatic and hydrophobic interactions are regarded presently as the texturization mechanism in this process. The recently suggested suspension (or filled "melt") model for biopolymer extrusion offered a new framework for testing extrusion of novel proteins. According to this view, the large differences between the association properties of proteins produce different types of aggregates. Some of them can be insoluble under extrusion conditions and act as a dispersed phase within the melt phase. The extrusion performance of a protein will thus depend on the amount of insoluble aggregate produced inside the extruder and on protein-protein interactions that occur after the superheated molten mass leaves it.