Establishing relationship between hydrophobicity and emulsification of caseins using generalized-regression-neural-network

Abstract: Yaks (Bos grunniens) from the Qinghai-Tibetan plateau are the sole source of milk of local inhabitants. In the past years, yak milk has attracted more and more attention, due to its increasing demand. Yak milk is widely used to produce butter, soft and hard cheeses, yogurt, milk powder, Qula, and casein-containing products. Caseins, the major protein in milk, are commonly used in the food, chemical, cosmetic, and pharmaceutical industries. Yak caseins are widely used to produce high quality food ingredients and soaps, glues, leather polishing reagents, and clothing, among others. However, compared to cow caseins, yak caseins have poor solubility, which affects the other functional properties. The poor solubility of yak caseins is mostly attributed to its conformation. Succinylation is the most frequently used modification method, which changes the conformation and increases the net charge of protein, which improves its functional properties consequently. It was indicated that the reaction conditions were mild and easy to control, the modified level was higher than other chemical modification, and its modification effect was outstanding.In this study, yak milk caseins were selected as materials and succinylation was used to modify the yak casein, and the effect of succinylation on casein emulsification and hydrophobility was studied. The GRNN was also used to build the model of relationship between pH, succinylated level, the main parameters of caseins hydrophobility, emulsifying properties, and it was proved to have good predictability.The results showed that the emulsifying properties of protein were affected by pH, spacial conformation, and hydrophobility mainly, and they were non-linearly related. The emulsification and hydrophobility of yak caseins were influenced by the degree of succinylation and pH. Above a pH of 5, with the increase of degree of succinylation, emulsifying activity of caseins increased. Near the isoelectric point, emulsifying activity was poorer, and then increased rapidly with the increasing of pH. The emulsion stability of modified casein was stronger with pH between 2-6, which changed slowly with pH between 6-11, and then increased greatly with pH at 12, and the emulsion stability of 10 min increased obviously. The values of native and ANS fluorescence intensity and maximum emission wavelength of native and ANS fluorescence of modified casein showed a more complex relationship with succinylated degree and the pH. GRNN had a good performance in deal with complex relationships of non-linear, which was used to establish the relationship model between succinlated level, pH, vital parameters of hydrophobility, and emulsifying properties in order to predict the emulsifying activity and emulsion stability with 10 min and 30 min. The error of predicted values was within 10%, so the results of prediction were credible. The model would save time and the cost of test about studying and predicting yak caseins emulsifying properties. The results could provide references for the study on emulsification of yak caseins and succinylation caseins.