Investigation On Non-enzymatic Browning And Nutritional Quality Changes Of Peach Juice During Processing And Storage

In this dissertation, peach juice was chosen as the raw material to study, the peach juice for different conditions of heat treatment (80℃,90℃and100℃) and storage treament (4℃,25℃and37℃), useing the scientific data analysis methods and the reasonable means models to explore the peach juice at different processing conditions and storage conditions of non-enzymatic browning kinetics and nutritional quality changes.The work is aiming to provide theory basis and technical support for peach juice industry development.Through the peach juice at different storage conditions of heat treatment and non-enzymatic browning reaction and nutritional quality of research, the conclusions are:1. The browning degree were increased0.185,0.221and0.276, L*values were decreased4.22,5.74and7.53, respectively. Chroma value and Hue angle were gradually decreased, Browning indexes (BI) were increased as the temperature increased. A420and color paraments well followed the combined kinetic models. Furthermore, the decline Vitamin C content during thermal process could be accurately described by the zero-order kinetic model (R2>0.894). Meanwhile, the combined kinetic model (R2>0.905) could properly express the gain of5-hydroxymethylfurfura (5-HMF) contents. The relationship between5-HMF and browning degree was satisfactorily fitted by means of quadratic model (R2>0.940) at the temperature of80,90and100℃.2. The sterilized by heat (condition) after the peach juice were stored at4℃,25℃and37°C conditions for40days d. The A420a*value, b*value and5-HMF content increased with thestorage temperature. However, L, the glucose content, Vc content and protein content decreased with the storage treament. At the end of storage period, the results showed that protein content were decreased22.65%.53.99%and64.56%as well as Vitamin C contents were decreased29.32%,39.65%and46.68%under storage conditions of4,25and37℃, respectively. The main losses of free amino acid were serine, alanine and aspartic acid. The results indicated that a*and b*values were well followed zero-order kinetic model (R2>0.859). Vitamin C could be supported by first-order model (R2>0.926). The combined kinetic model could be applied to browning degree (A420), L*values and5-HMF (R2>0.916). In addition, the relationships between5-HMF and A420and5-HMF and a*value were satisfactorily fitted by means of Quadratic model (R2>0.875and R2>0.866, respectively). Therefore, the quality changes of peach juice would be expressed by kinetic models reasonably.3. Microwave treatment the peach juice, detection and analysis of peach juice under different storage conditions of physical and chemical indicators, nutrients and aroma composition changes.The result showed that browning degree index increased by0.14,0.33and0.56at the storage tempetrature of4,25and37℃, respectively. The content of total sugar was decreased by49.06%,53.59%and57.19%, vitamin C was46.27%,43.05%and56.20%, protein was31.82%,57.14%and64.00%. There was no significant change in the content of total acid before and after storage. Meanwhile, the effect of storage time and temperature on the browning degree, pH, total acid, Vitamin C, protein and total phenol content were highly remarkable (p<0.01). The variety of aroma composition of peach juice was up to35. For the peach juice before storage, the aroma was very good, characterized by Undecan-4-olide and5-Decanolide which reached1.25%and5.45%. While after a month of storage, the amount of identified aroma components declined to79.90%,60.14%and54.59%of the total mass fraction at4,25and37℃, respectively. Therefore, low temperature storage could keep the quality of peach juice.