Research On Nonenzymatic Browning And Control Technology Of Dangshan Pear Juice Concentrate

Dangshan pear is the special fruit of Anhui province, it's culture area was more than 335 Km², production more than 1000 thousands tons a year. Beside saled as fresh fruit,the rest of 30% pear was processed into pear juice. Accord to the procession technics, after the ultra-filtration(UF) and resin decoloring, the color index (T₄₄₀) of pear juice was about 90%, and than it was concentrated to 70Brix^o, T₄₄₀ decrease to 75%. Newly processed pear juice concentrate(PJC) can meet the national import standed(T₄₄₀>45%), but T₄₄₀ decreased quickly during storage and transport, it decreased to less than 30% at 37℃in one week, these influenced the quatity, price and competition of PJC.To solve the browing problem of PJC during storage, as the main research object of the key items of production procession of Anhui province:"Key procession technology and its industrialization of PJC". In this research, firstly the browing type(enzymatic,non- enzymatic) of PJC during procession was distinguished, then the emphases was put on discuss the mechanism and kinetics of NEB during storage, at last experiment was carried out to control the NEB of PJC by combine ion exchange and absorbent technolnogies. The experiments investigation indicate:1. During the process, the browning was mainly EB before pre- concentration; NEB and EB contributed together between pre- concentration and UF; after UF it was NEB mainly . The browning during storage was NEB mainly,. EB had no significantly effcct.2. In the NEB of PJC during storage, the concentration of total AA,sugar and total phenols decreased signficantily ,and they are correlated with browning index(A₄₄₀) , the relationship model was exponential type,linely type,linely type separately.The mechanism of NEB at different temperature were studied by building PJC models, the result was : Maillaid reaction was the main fact of NEB at 50℃, the arrtribuit of Maillaid was 4 times of caramelization, phonel oxidation had no effect; at 30 and 37℃, the Maillaid reaction was the only fact, caramelization and phonel oxidation had no effect. As the reagent of Maillaid reaction and caramelization, the contribution of sugar and amino acid were investigated, the result showed: the sequence of sugar's contribution to NEB was fructose>glucose>sorb> sucrose; the sequence of amino acid's contribution to NEB was Asp>Ala,Glu,Thr>Val>Lys,His,Met,Leu,Arg>Ile>Phe,Cys>Pro.3. Browning index (A₄₄₀) of PJC increased with both time and temperature, according to two stage combined reaction kinetic, the browning rate constants(K) increased with temperature. Browning activation energie of the PJC was 7.05 kcal/mol. 5-Hydroxy -methylfurfural (5-HMF) also increased with both time and temperature, the correlation between 5-HMF concentration and A₄₄₀ is positive. Influence of light on browning was negligible, while air was significant in early time.4. Combining ion exchange and absorbent technolnogies can control NEB effcctly and prolong storage time of PJC. Treating 20Brix^o UF pear juice treated with FPC-21 to reduce the pH to4.0-4.1, then treated with XAD-16 to rise color(T₄₄₀) up to 80%, and concentrated to 70Brix . After transported to the port by ship at 37℃in 35 days, it's color >45%, can meet the export regulation.