Studies On Producing Cloudy Apple Juice And Storage Stability Of The Products

The research was conducted to develop two kinds of processing techniques used for cloudyapple juice prouduction. Anti-browning reagents were used in one procedure and steam heatingduring crushing was used in another. Color and cloud stability of two kinds of products werestudied.There was 84.7% enzymatic browning occurring during crushing when cloudy apple juice wasmade, so anti-browning reagents should be added during crushing. The inhibition ability of somestudied anti-browning reagents was: 0.1% Vc > 0.1% sodium metabisulfite > 0.1% kojic acid >0.1% CaCl2 > 0.005% cysteine > 0.1% NaCl whereby the inhibition abilities depended largely ontheir concentration. The combination of Vc or cysteine with NaCl was effective in inhibitingenzymatic browning, but when cloudy apple juice containing cysteine was heated, its color turnedred and this limited the use of cysteine in cloudy apple juice. The combination of 0.044% NaClwith 0.0125% ~ 0.025% Vc could inhibit the enzymatic browning during crushing, and in thesame condition the enzymatic browning in apple puree and juice was avoided for 5-10 min and40-95 min respectively.When apple juice was heated at 90℃ for more than 15s, the polyphenol oxidase (PPO) wascompletely inactivated and for apple puree, the heating time was more than 20s at 90℃ andmore than 10s at 95℃. When apple juice was heated at 70℃ or 80℃ for 45s, PPO was notcompletely inactivated. When apple juice including anti-browning reagent was heated at 90℃for more than 10s , PPO was completely inactivated. In addition, though apple juice includinganti-browning reagent was heated at 80℃ for more than 30s PPO was not completelyinactivated,however, the enzymatic browning would not occur due to the anti-browning reagentand low pH of apple juice.Heating apples in water of 45℃ for 45 minutes before crushing could improve the color andcloud stability of cloudy apple juice. Since the optimum temperature for methylesterase(PME)was 40 ℃, when apples were put in water of 45℃ for 45 min, PME caused only partialdemethylation of pectin, which led to more negative charge incorporated into pectin by exposingmore –COOH of galacturonic acid residues. As a result, both the electrostatic repulsion ofparticles and the combination in particles of the protein core with positive charges between thepectin with negative charges were enhanced, thereby the color and cloud stability of cloudy applejuice were improved. Longer heating time would cause lower methoxy content of pectin in applesby the action of PME and the pectin would be liable to be hydrolyzed by polygalacturonase(PG).As a result, the molecular weight of pectin decreased as treating time increased which caused thedecreasing in viscosity of cloudy apple juice. Though with higher Zeta potential, juice made fromapples heated for 60 min before crushing had poor cloud stability. More pectin was released fromcell wall and tissue of apples as a result of higher crushing temperature. More pectin in juicecaused higher viscosity and better cloud stability. When crushing temperature was above 40 ℃,the color of juice would become brown due to the degradation of Vc in juice. Considering thecolor and cloud stability, the better crushing temperature was 30℃. Based on the studies above,improved processing conditions were determined.An apple cruching machine was designed and used to study processing of juice using steamheating during crushing. The main browning occuring during the crushing of apples belongs toenzymatic browning, but non-enzymatic browning became prominent along with increasedtemperature and prolonged heating time. The color of juice was affected markedly by the highesttemperature of purees. When purees were heated above 92℃, though more Vc was lost for juicesmade from purees, juice had more phenolics and better color stability due to poor activity of PPOwhich was inactivated by heating and low pH environments. Heating released more pectin frompurees to juice, and avoided decreasing of viscosity of juice due to the hydrolysis of pectin by PG.In addition, heating purees could reduce the size of particles in cloudy apple juice to improve thecloud stability of juice. The optimal temperature for cruching apples with machine designed byourselves was 95℃ based on the experiment, standardized experiment datas and the calculationusing computer with matlab software. The non-enzymatic browning occuring during sterilizationwas mainly caused by the oxidation and polymerization of phenolics, while the degradation of Vc,millard reaction and caramelization contributed little to the browning occuring in juice. Thenon-enzymatic browning occuring during sterilization could be avoided by adding 0.0060% Vc tojuice. Based on the studies above, improved processing conditions were determined.When phenolics were analyzed by HPLC technique, volatile flavor compounds were analyzedby GC/MS aided by HP-SPME. Results showed that Vc, phenolics and volatile flavor compoundsin apples were lost during processing. Loss of Vc and phenolics was mainly caused by heatingpurees and juices at above 85℃ and by remaining them in discarded apple residues. Loss ofvolatile flavor compounds was mainly caused by heating purees and juices at above 85℃. Lessloss of Vc and phenolics during the processing of using steam heating was due to higher yield ofjuice and less discarded apple residues, and less loss of volatile flavor compounds during theprocessing using anti-browning regeants was due to less heating intensity.Genuine, semi-modeled and modeleded systems were made to study the factors which affectedthe formation and growing of particles in cloudy apple juice during the processing. Pectin andproteins were extracted from apples to make modeled systems. There were three factors affectingthe formation and growing of particles in cloudy apple juice. Firstly, insoluble pigment caused byenzymatic browning could increase the turbidity directly or in combination with other particles.Secondly, protein-phenolic complex could congregate to larger particles. When the cloudy applejuice was heated, all the factors contributed to particle size enlargement. The formation andgrowth of particles in three systems were markedly inhibited by the pectin in them. When themodeled system was heated, more binding sites in protein for phenolics were exposed and theincrease in turbidity for system was remarkable.According to the yield, color and cloud stability, juice made by processing using steam heatingwas the best, juice made by original processing was the worst, and juice made by processingusing anti-browning regeants was fair.120 days storage experiment of juice at 4℃,22℃ and 40℃ was conducted. The browning ofcolor, degradation of Vc and phenolics became acute along with increased temperature andprolonged storage time. The speed of degradation was quick during initial period of storage andthen slowed down, and the color of juice became more red, dark and yellow. For the juice madeby processing using anti-browning regeants, a more serious browning and yellow color werefound as a result of more loss of Vc. Non-enzymatic browning occuring during the storage wascaused mainly by the degradation of Vc and the oxidation polymerimation of phenolics, and itcould be controlled by storing juice at lower temperature. Non-enzymatic browning occuringduring the storage of the juice made by processing using anti-browning regeants was mainlycaused by the oxidation and polymerimation of phenolics and it could be controlled by adding0.006% Vc or storing juice at lower temperature. The loss of epicatechin, procyantodins,chlogenic acid and the mean polymerization degree of tanin became more along with increasedtemperature and prolonged storage time. Vc could protect phenolics, but when more Vc wasadded to juice, browning of juice caused by the degradation of Vc would affect negatively thecolor of juice. The browning had a poor correlation with the degradation of chlogenic acid andwas affected more by epicatechin and tannin. Amino acids also were involved in the browningreaction and Millard reaction was indistinctive.The cloud stability of juices during storage was studied by optical microscope, electronmicroscope and particles distribution analysis combined with component analysis. The cloudstability of juice made by steam heating was better than that of juice made by processing usinganti-browning regeants. At the beginning of storage, the turbidity of juices decreased quicklybecause particles of larger size in juice congregated and sedimented and since the larger particlesat the upper of bottle were less and less, the sedimenting speed of particles decreased. Theoxidation and polymerization of phenolics in juice became acute along with increasedtemperature and prolonged storage time and this caused the formation of insoluble brownpigments. Therefore, browning occured while turbidity increased as a result of formation of somenew small particles. The addition of Vc to juice could inhibit the oxidation and polymerization ofphenolics to avoid browning and the formation of insoluble new small particles, and reduced thechange of turbidity of juices during the storage.The sediment of juice made by using anti-browning regeants was complicated and consistedmainly of proteins, carbohydrate (starch, celluse, semi-celluseand and pectin), phenolics (flavanolglycosides, epicatechin, chlogenic acid, tannin), 5-hydroxymethyl-furaldehyde (5-HMF). Besidesthe proteins of 21-31kDa reported in post-haze formation in clarified apple juice, there were otherproteins in the sediment of cloudy apple juice during storage.The sediment mainly formed by theassembling and settling of original particles at the beginning of storage in juice. The new smallparticles formed by the jointing of phenolics after polymerization with proteins or amino acidsand post-haze that was similar with in clarified apple juice also contributed to the formation ofsediment. The cloud stability of cloudy apple juice would be more improved by adding 0.05%(w/v)CMC to juice, but agitation after CMC addition would affecte negatively the colorstability of juice due to the loss of phenolics and Vc.The cloud stability of juice containing CMCwas improved by increased viscosity of juice and increased Zeta potential of particles in juice,and for juice containing guar gum, it was improved by increasing viscosity of juice.Further work should be done such as analyzing the pigments caused by browning reaction,analyzing the change in anthocyanins and polymerization degree of condensed tannins during thestorage of cloudy apple juice, and the change in volatile aroma composition during the processesof cloudy apple juice.