Application of jet-cooking in preparation of digestible corn protein concentrates

Abstract: Corn protein concentrates (CPC) were prepared continuously from corn gluten meal (CGM). Firstly, sub-critical fluid and α-amylase were used to remove crude fat and degrade starch. Then, the resultant protein suspension was concentrated and separated by ultra-filtration membrane. The ultra-filtration membrane process was used to remove the impurities produced by the first process such as soluble carbohydrate. The concentrated protein suspension was incubated with 0.2 M citric acid and treated by jet cooking device at 140℃ for 90 s. Finally, 3 samples could be acquired by spray-drying process. In order to study the effect of jet cooking on the functional properties of CPC, solubility profile, deamidation degree, and amino acid composition were investigated. Moreover, the digestibility in vitro and the antioxidant activity of digestive product were investigated. We expected to provide an effective and continuous process technology for the application of CGM, and prepared a kind of CGM which exhibited excellent functional properties and digestibility in vitro. The results showed that protein content of CGM was improved after the removing of crude fat and starch. However, there was no difference among CPC, JC-CPC (jet cooking CPC) and HT-CPC (heat treatment CPC) in the amino acid composition, protein content and recovery rate (P>0.05). The results of solubility suggested that CPC, HT-CPC and JC-CPC exhibited a typical U-shaped solubility curve, with the minimum at the pH value of 5.0-6.0 and gradually increasing at the pH value below 4.0 and above 7.0. When the pH value was below 4.0 and above 7.0, the solubility of JC-CPC was superior to CPC and HT-CPC. These results may be ascribed to the effect of deamidation that led to translate insoluble amino acid (Asn or Gln) to soluble amino acid (Asp or Glu), and the high temperature and high shear force during the treatment of jet cooking process which made the protein unfold and disaggregate. And owing to the effect of high temperature and high shear force during the jet cooking process, the foaming capacity and the foaming stability of JC-CPC were improved significantly (P<0.05) compared to CPC and HT-CPC. In the process of digestion in vitro, the nitrogen release of 3 samples increased rapidly at the beginning, and then gradually slowed down. After digestion, the nitrogen release of JC-CPC cloud reached up to 62.05%±0.75%, higher than the CPC (21.02%±0.19%) and HT-CPC (40.25%±0.72%) (P<0.05), and the degree of hydrolysis cloud reached up to 24.02%±0.49%, higher than the CPC (9.23%±0.45%) and HT-CPC (14.52%±1.26%) (P<0.05). These results were mainly due to the improvement of protein's solubility and the protein unfolding which may expose more protease binding sites and hence led to enzymatic hydrolysis more efficient during the jet cooking process. In addition, the reducing capacity of digestive product of JC-CPC was better than that treated by alcalase alkaline protease (P<0.05), while the 1,1-Diphenyl-2-picrylhydrazyl (DPPH) inhibition of JC-CPC after pepsin and trypsin treatment was similar to that treated by alcalase alkaline protease. We can draw a conclusion that the product of JC-CPC after digestion in vitro possesses good antioxidant activity and physiological activity which may be beneficial to human beings, as well as the product treated by alcalase alkaline protease. It also means that the digestive product of JC-CPC cloud can be directly absorbed by human beings in the gastrointestinal tract. JC-CPC exhibits excellent functional properties, and digestibility property in vitro is attributed to the effect of jet cooking. The outcomes of the above research may prove a valid way to the application of CGM in further processing of plant proteins.