喷射蒸煮技术在制备易消化玉米浓缩蛋白中的应用

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

为了提供一种具有良好消化性的玉米蛋白,该研究以玉米黄粉(corn gluten meal,CGM)为原料,利用亚临界脱脂及酶解超滤技术制备了一种蛋白纯度较高的玉米浓缩蛋白(corn protein concentrates,CPC),并重点考察了制备过程中喷射蒸煮对玉米浓缩蛋白功能性质及消化性的影响。研究结果表明,经喷射蒸煮处理后的玉米浓缩蛋白(jet cooking corn protein concentrates,JC-CPC),普通高温处理的玉米浓缩蛋白(heat treatment corn protein concentrates,HT-CPC)以及未经高温处理的玉米浓缩蛋白(CPC),三者在蛋白质质量分数及氨基酸组成上无明显差异(P>0.05)。但JC-CPC的溶解性及功能性质(持水性、起泡性及泡沫稳定性)均显著高于CPC和HT-CPC(P<0.05)。体外模拟消化试验结果表明,JC-CPC的水解度(24.02%±0.49%)明显高于CPC和HT-CPC(分别为9.23%±0.45%和14.52%±1.26%)(P<0.05),其可溶性氮释放量(62.05%±0.75%)亦高于HT-CPC(40.25%±0.19%)、JC-CPC(21.02%±0.72%)(P<0.05)。同时,JC-CPC消化产物的抗氧化试验结果表明,其消化产物具有较高的还原力及1,1-二苯基-2-苦基肼(1,1-Diphenyl-2-picrylhydrazyl,DPPH)自由基的清除能力。因此,利用喷射蒸煮技术,结合亚临界及超滤除杂技术能够为食品工业提供一种具有良好消化性的玉米浓缩蛋白,有望为玉米黄粉的利用提供一条有效途径。

Corn protein concentrates （CPC） were prepared continuously from corn gluten meal （CGM）. Firstly, sub-critical fluid and a-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 Gin） 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.