NUTRITIONAL EVALUATION OF BLENDED FOODS MADE WITH A LOW-COST EXTRUDER COOKER

Development by extrusion of soyabari snack sticks: a nutritionally improved soya-maize product based on the Nigerian snack (kokoro)

A nutritionally improved local snack compared to existing kokoro has been developed by extrusion cooking of different formulations of maize, soybean and condiments such as pepper, onion, salt, palm oil, plantain and banana. The improved snack was named as the 'soyabari snack stick'. The chemical composition of representative extruded products indicates a high level of crude protein, fat, energy, available lysine and improved in vitro digestibility compared to the usual maize-based products. The level of stachyose and raffinose were greatly reduced in the extruded products compared to raw soya. Formulations using various additives yielded products suitable for different consumers' preferences such as hot, sweet, bland, gritty or crispy and acceptable to taste assessors. Soyabari snack sticks were equally acceptable as Bombay mix, a product on the market in London. Sensory analysis showed no significant differences in the two products but the crude fibre content of Bombay mix was higher while the protein was slightly lower than for soyabari sticks. Local ingredients can produce acceptable extrudates.

Effect of extrusion processing on the nutritional quality of protein in rice-legume blends

The effect of extrusion processing using Wenger X-5 extruder on the quality of products of rice-legume (75:25) blends was investigated. The products were palatable and had a good texture. The nutritional quality of protein in the extrudates was significantly improved. The protein efficiency ratio values of rice-soybean, rice-bengal gram and rice-black gram products were: 2.25, 2.30 and 2.28 as compared to 2.10, 1.89 and 1.98 for the respective raw blends. Extrusion processing reduced the phytates in the products to the extent of 20.3 to 26.8%.

[Effect of various extrusion conditions on the protein quality of soybean and whole rye meal]

Using a Creusot-Loire twin-screw extruder (Type BC 45), ground soy bean and whole rye meal were extruded under various processing conditions (12% and 18% water content in the raw material, 129 degrees C and 165 degrees C product temperature in the case of soy bean, 12% and 18% water content, 165 degrees C product temperature in the case of rye, screw speed of 150 R/min, for all samples). The nutritional protein quality (apparent protein digestibility PV, net protein utilization NPU, and biological value BW) of the extrudates was determined by the nitrogen balance technique in growing rats. Compared to the untreated raw material no decrease in PV or NPU was noted for extrudates made from soy bean or rye. Extrusion of ground soy bean at 165 degrees C and 18% water content caused a significant decrease of BW from 68% to 64%. The lower water content (12%) induced a slight improvement of PV in soy extrudates and of NPU and BW in rye extrudates. The results indicate that the extrusion at low water content and moderate temperature can safely be used to process ground soy bean and whole rye meal without and damage to the nutritional protein quality.

Food extrusion

Extrusion processing has become an important food process in the manufacture of pasta, ready-to-eat cereals, snacks, pet foods, and textured vegetable protein (TVP). An extruder consists of tightly fitting screw rotating within a stationary barrel. Preground and conditioned ingredients enter the screw where they are conveyed, mixed, and heated by a variety of processes. The product exits the extruder through a die where it usually puffs and changes texture from the release of steam and normal forces. Mathematical models for extruder flow and torque have been found useful in describing exclusion operations. Scale-up can be facilitated by the application of these models. A variety of food extruder designs have developed. The differences and similarity of design are discussed. Pertinent literature on the extrusion of cereal/snack products, full-fat soy, TVP, pet foods (dry and semi-moist), pasta, and beverage or other food bases are discussed. In many of these applications, the extruder is a high temperature, short time process which minimizes losses in vitamins and amino acids. Color, flavor, and product shape and texture are also affected by the extrusion process. Extrusion has been widely applied in the production of nutritious foods. Emphasis is placed on the use of extrusion to denature antinutritional factors and the improvement of protein quality and digestibility.