Preparation Of Clear Blackberry Juice

Blackberry(Rubus fruticosus L.) is a burgeoning berry fruit, which is highly flavored and colored and is called"purple life fruit"for its abundant nutrition. The yield of blackberry in China reached 10,000 tons in 2006, and China has become the first largest producer of blackberry in Asia. Blackberry is primarily a table fruit, but most of blackberries are processed into many products due to its badly storage performance. Clear blackberry juice, with highly acceptable aroma, can be used in various foods and drinks and can be well developed. However, clear blackberry juice has not been commercially successful due to its excessive haze and sediment formation with color loss. In order to improve the qualities of clear blackberry juice, it is essential to study systemically on the processing and qualities of clear juices.The objective of this dissertation is to develop an enzymatic technology for processing blackberry juice, prepare carboxymethyle chitosan to clarify blackberry juice and investigate the stability of clear blackberry juice. The main results are as follows:The effect of steam blanching on the polyphenol oxidase (PPO) was studied and the results showed that PPO from blackberry pulp had a relatively low thermal stability. The optimum parameters of steam blanching process were confirmed with blanching for 2 min to inactivate PPO when the central temperature of blackberry was 52℃. Moreover, steam blanching could not only inactivate PPO, but also induce a significant recovery increase of anthocyanins and polyphenols, in relation to the higher quality of blackberry juice.The mechanism for the degradation of anthocyanins by PPO was investigated by establishing a model system. The loss of the colour in this model system containing PPO and blackberry anthocyanins indicated that PPO could act directly on these pigments. However they remain fairly poor substrates of PPO. The rate of anthocyanin degradation was stimulated by the addition of non anthocyanin polyphenols. Anthocyanins were oxidised via the enzymatically generated o-quinone by coupled oxidation mechanism.The effects of different commercial pectinolytic enzyme preparations on blackberry juice quality were determined. The enzyme preparations affected the clarity and contents of anthocyanins and polyphenols in the juice due to different activity profiles of these enzyme preparations. The commercial pectinase named Klerzyme 150, which contained almost no anthocyaninase activity, had a desirable effect on the yield and quality of blackberry juice. Studies on the uniform design for Klerzyme 150 enzyme revealed that the optimum conditions were 0.063 % (v/w), 44 oC and 110 min for enzyme dosage, reaction temperature and reaction time, respectively.Chitoan was modified to carboxymethyl chitosan, which had different degree of substitution. The chemical structure was characterized by the combination investigation of FTIR, XRD, TG and NMR and the compound were identified as N,O-carboxymethyl chitosan. Carboxymethyl chitosan was used to clarify the blackberry juice and the results showed that the clarity of blackberry juice was related to the degree of substitution. When the degree of substitution was 0.86, carboxymethyl chitosan could clarify blackberry juice greatly. The characteristics of clear blackberry juices clarified with chitosan and carboxymethyl chitosan were compared. It indicated that the juice clarified with carboxymethyl chitosan had much less potein and polyphenols.Clarification mechanism of blackberry juice by carboxymethyl chitosan was investigated. There existed interaction of hydrogen bond between -COOH,-NH2,-OH of carboxymethyl chitosan and blackberry protein and blackberry polyphenol, which was confirmed by FTIR, XRD, TG and Zeta potential. Carboxymethyl chitosan could absorb protein and polyphenol in blackberry to produce primary ?ocs and then bridge among these primary ?ocs to form bigger flocs and thus clarify blackberry juice.The results of storage tests at different storage temperature indicated that anthocyanins were prone to degradation. It was found that the thermal degradation of anthocyanins followed first-order reaction kinetics. During storage, the browning index and polymeric color increased, while the color density decreased. Storage at low temperature was good for the color stability of blackberry juices.According to the analysis of the main components of sediment of clear blackberry juice after 6 months storage, the main aspects influencing sedimentation of blackberry juice were discussed. There were 50.39% of polyphnols, 15.67% of protein, 13.19% of carbohydrates, and 1.73% of ash. The haze of clear blackberry juice was mainly the type of tannin and protein-tannin haze. The second sediment contained condensed tannin when analyzed the composition with NMR. Anthocyanin and catechin could condense to produce tannin, which could increase degree of polymer and/or interact with protein to produce sediment.The polyphenols in blackberry fruit were isolated and characterized by high performance liquid chromatography (HPLC) with UV-visible detection, electrospray ionization mass spectroscopy (ESI-MS). Four defined anthocyanin pigments were detected, all of them containing cyanidin (Cy) as aglycone. Cy 3-O-glucoside was the major pigment constituting 76.92% of the anthocyanins in blackberry fruit followed by Cy 3-O-dioxalylglucose (14.46%),Cy 3-arabinoside (3.29%),and Cy 3-malonylglucos(e2.86%). Flavonols (primarily quercetin glycosides) were the major flavonols in berries pulp, whereas procyanidins (catechin and epicatechin) and benzoic acid predominated in seeds.Clear blackberry juice concentrates and their rheological properties were studied. The concentrates were predominantly Newtonian over the range of temperature and solids content studied. The effect of temperature and solids content on the viscosity of clear blackberry juice concentrates could be characterized by a mathematical model.The volatile compounds of blackberry juice during processing were concentrated by SPME, separated and identified by GC-MS. There were 65 kinds of compounds in volatile fraction of blackberry juice, and the main components were alcohols and aldehydes. The kinds of volatile compounds were decreased by 27% and 2-Hexenal became the most compounds in blackberry juice concentrates. Because of fat hydrolysis, fatty acids oxidation and Maillard reaction, furan and some alcohols produced during juice processing were also detected in original and blackberry juice concentrates.