Protein Quality Evaluation of Enteral Foods

This chapter describes the protein quality evaluation of the enteral foods developed in this project. The protein quality of a food product not only depends on the nature of ingredients used, but also on the processing method followed. Although nutrient losses during processing can be minimized by optimizing processing methods, some amount of nutrient losses specially that of heat-sensitive nutrients are inevitable. Studies have shown the losses of certain amino acids such as lysine and other amino acids during heat treatment, thereby lowering the protein quality (Ilo and Berghofer, 2003; Yeung et al., 2006). Studies have also suggested supplementation of amino acids in infant food and enteral foods to preserve the protein quality (Sarwar et al., 1993; Sarwar and Peace, 1994). The food formulations based on cereals, legumes, and proteins of animal origin that are blended in suitable proportion and fortified with vitamins and minerals may generally be termed as nutritionally balanced foods. However, considering the processing loss, it is suggested that the nutritional quality of a food protein should be evaluated by in vitro test as well as be confirmed by an appropriate in vivo test (Vanderveen, 1981). Hence, it is customary that whenever a new food is formulated, its nutrient analysis, growth-promoting quality, and related aspects of protein quality are determined by animal feeding trials (Pellet and Young, 1980; Sarwar and Peace, 1994). Usually, protein efficiency ratio (PER) of the food is determined in weanling rats, and metabolic studies are carried out on growing rats. The data generated from the PER and metabolic studies are usually utilized to evaluate the nutritional compatibility of the food protein for humans (FAO, 1991).

Generally spray-dried and roller-dried malt foods have slightly lower PER than the malted cereals and legume-based foods (Rao et al., 1976; Wondimu and Malleshi, 1996) that need cooking prior to feeding. This might be due to the Maillard Reaction — the reaction between malt sugar and amino acids — that occurs during spray drying, and thus resulting in decreased bioavailability of lysine (Dworschank, 1980; Lowry et al., 1990, Yeung et al., 2006). Any damage to the essential amino acids such as lysine, methionine among others is reflected in low biological value of the proteins. It is desirable that the enteral food proteins should be of high biological value. Although the main ingredients of enteral foods in the present study are malted cereals, legumes, milk, and egg, it was interesting to know the nutritional quality of the food protein, because these ingredients had further undergone processing. Hence, the protein quality of the enteral foods was evaluated by chemical analyses (in vitro) of its amino acid profiles as well as by conducting animal feeding (in vivo) experiments. The details of the chemical analyses of amino acid profiles of the enteral food proteins are discussed in Chap. 4. The protein quality as assessed by protein efficiency ratio (PER), net protein ratio (NPR), biological value (BV), true digestibility (TD), net protein utilization (NPU), and protein digestibility corrected amino acids score (PDCAAS) conducted in animal models is presented in this chapter.