Experimental Study On The Non-enzymatic Browning Of Amorphous Powder And Juice

The non-enzymatic browning of amorphous powders and juice is a problem closelyrelated to many industries and the quality of products. It has harmful influence on theprocessing and shelf life, and ruins the taste and reduces the nourishment and the quality ofproducts. It is a valuable research subject not only academically but also practically to studythe non-enzymatic browning of juice and amorphous powders in order to find way to controlit and keep them in safe state.In this study two kinds of amorphous skim milk powder, PVP and some kinds of juiceare selected as samples. The effects of storage conditions (storage temperature, water activityand storage time) on non-enzymatic browning of skim-milk powder and PVP are investigatedexperimentally. The relationship between non-enzymatic browning index and T-Tg (T is thestorage temperature and Tg is glass transition temperature) is examined.The effective factors such as temperature, pH, sugar (soluble solid substance) content,and metal ion to the non-enzymatic browning of juice are investigated experimentally. Theresults show that temperature has great influence on the stability of juice during storage, andthe higher temperature, the worse the stability of juice. Sugar content also has notableinfluence on it, and the higher sugar content, the worse the stability of juice, pH is positivelycorrelated with A₄₂₀ within 3 weeks in storage at 25℃, whereas pH is negatively associatedwith A₄₂₀ after 3 weeks storage. Ca²⁺ can decrease the rate during storage, while Fe³⁺, Fe²⁺and Cu²⁺ can accelerate it. The optimal combination is: the HSO₃^- content of 0.003mol/L, theVc content of 0.009mol/L, the Ca²⁺ content of 0.04mol/L, pH value of 2. The amount of5-HMF produced by the non-enzymatic browning of juice increases linearity with the heatingtime. The effects of Ultra-high pressure treatment on non-enzymatic browning of pear juiceare investigated experimentally. The results show that the treatment has no remarkable effecton non-enzymatic browning of juice.The glass transition temperature is usually determined experimentally, but it is timeconsuming and tedious to get the glass transition temperature by traditional methods. Theinstruments are expensive also. It is necessary to find a method to calculate glass transitiontemperatures for biopolymers. The additive group-contribution technique is used and acomputer program is written to compute the glass transition temperatures of biopolymers. Theresults from the calculations are in good agreement with experimental data. A quantitative expression is established to relate Tg and water content of some typical starches, and the costand time for conducting such experiments are saved.This study makes a contribution to the knowledge of non-enzymatic browning and theireffective factors of amorphous powders and juice, guides the production, process and storageamorphous powders and juice, and provides basic information and useful data to controlnon-enzymatic browning and to study further.