Search

The effects of whey protein concentrate (WPC) on the formation of soluble protein complexes and yoghurt texture were evaluated. Skim milk (SM) and skim milk enriched with 1% WPC (SM + 1%WPC) or 2% WPC (SM + 2%WPC) were left unheated or heated and then made into yoghurt gels. Yoghurt prepared from heated SM + 2%WPC had significantly higher storage modulus, water holding capacity and firmness values and a denser microstructure than those prepared only from skim milk. Electrophoretic analysis of the milk showed that the level of β-lactoglobulin and κ-casein in the serum phase increased with increasing WPC concentration, indicating that the content of disulfide-linked β-lactoglobulin and κ-casein was higher in SM + 2%WPC than in SM, suggesting that more soluble protein complexes had been formed. Consequently, yoghurt prepared from heated SM enriched with WPC may have more bonds and more protein complexes in the protein network than yoghurt prepared only from SM, thus resulting in firmer gels. Practical applications Yoghurt, one of the most popular fermented milk products, is of high economic importance to the dairy industry worldwide. In particular, high-protein yoghurt, such as Greek-style or set-type yoghurt, has been driving its ongoing popularity over recent years. In current industrial production of high-protein yoghurt, protein fortification and heat treatment of milk are two of the most important processing parameters affecting yoghurt texture. Whey protein concentrate has been added to milk to reduce whey separation and to increase the firmness of the yoghurt. From a technological point of view, the interaction of the denatured whey proteins with casein micelles or with κ-casein in the serum phases is regarded as responsible for obtaining a good yoghurt structure. The present research has shown that it is possible to produce yoghurt with a range of textural properties by precisely controlling the rate of whey protein fortification during its manufacture. Therefore, this study provides a better understanding of the effect of WPC fortification and aims to extend this insight for the production of good-quality yoghurt.

Properties of yoghurt extremely depend on the application of heat treatment to milk prior to manufacture. After heating the milk, denatured whey protein and casein makes complexes which dramatically improve the yoghurt texture such as firmness and water holding capacity etc. The formation of complexes, micelle bound or soluble whey protein/k-casein complexes, and their localization between casein micelles and serum depends on the physical properties (heat treatment, pH, compositions) of milk. We review the formation of these complexes and their effect on the physical, rheological and microstructural properties of acid milk gels. In order to investigate the interactions of denatured whey protein-casein, the formation of covalent and non-covalent bond namely thiol/disulphide, hydrophobic and electrostatic etc. are reviewed, with the emphasis on acid gelation and final yoghurt texture. This review summarizes the different factors and interactions on the formation of the micelle bound complexes or soluble denatured whey protein/k-casein complexes in heated milk and how these complexes affect the yoghurt properties. This information could be fundamental knowledge for developing a desirable yoghurt texture, may have potential interest for future research.

Here, we investigate the effects of pH adjustment before heating milk on the textural properties of whey protein enriched yogurt. Whey protein enriched skim milk was adjusted to pH of 6.3, 6.7, and 7.1 followed by heating at 85 °C for 30 min. Yogurts prepared from milk heated at pH 6.7 showed remarkably higher G′ (storage modulus) values, water holding capacity and firmness compared to those prepared from unheated milk, or milk heated at pH 6.3 or 7.1. A relatively more compact protein network was observed in the yogurt made from milk heated at pH 6.7. Heating milk at pH 6.7 formed both whey protein-associated casein micelles (WPA-CM) and soluble whey protein/κ-casein complexes (SWP-CC), resulting in the presence of numerous aggregating particles, which was responsible for the firmer yogurt gel. Heating milk at pH 7.1 (mostly SWP-CC) resulted in higher yogurt firmness than heating at pH 6.3 (mostly WPA-CM). Practical applications Whey protein fortification and heating milk improve yogurt texture. However, different pH values of the milk before heating and whey protein fortification affect the properties of the yogurt. Variation of milk pH before heat treatment affects the degree of association between denatured whey proteins and casein micelles. As a result, inconsistencies occur in yogurt gel texture. This study showed that yogurt made from milk heated at pH 6.7 had increased firmness and water holding capacity compared with that when the milk was heated at pH 6.3 or 7.1. The pH of milk naturally changes slightly throughout the year, which in turn might affect yogurt firmness. Therefore, milk pH is an important parameter which needs to be adjusted to produce uniform quality yogurt to obtain a well-accepted commercial product.

The chemical, physico-chemical and functional properties of flour and starch from three varieties of jackfruit seed were analyzed in this study. Starch was isolated using distilled water, alkaline and α-amylase enzyme. All varieties of jackfruit seed flour had moisture content 6.28-9.16%, protein 9.19-11.34%, fat 1.18-1.40%, ash 1.53-2.66%, amylose 26.49%-30.21% and starch contents 81.05%-82.52%. Gala variety had highest amount of water soluble index, swelling water capacity and water absorption index than Khaja and Durasha varieties. On the other hand, isolated starch varied 8.39 to 12.20% moisture, 1.09 to 3.67% protein, 1.18 to 1.40% fat, 0.03 to 0.59% ash content. Starch isolated with distilled water had higher protein content, yield, amylose and total starch than starch isolated with alkaline and enzyme. However, purity was depended on the variety and extraction conditions. Enzymatic method gave highest amount of water absorption index and water soluble index as compared to distilled water and alkaline method. Results from this study suggest that jackfruit seed flour can be used as partial replacement of wheat flour and good source of starch.