| Xinjiang is a place rich in apricot resource, the apricot used in this research is one of the apricots produced in Luntai which usually called "small white apricot" by local people. This paper focused on the processing technologys and understanding the reasons for the browning and suspension stability during storage, these are the main technical difficulties in the manufacture of juice. Some important analytical properties were determined as well as the process, formula and the effect of different stabilizers on the stability of apricot nectar were investigated. Furthermore, the mechanism and kinetics of non-enzymatic browning of apricot nectar during processing and storage were measured and discussed. The main contents and conclusions were as follows:(1) The analytical properties of concentrated apricot pulp were determined by HPLC, laser particle size analyzer, viscometer and other equipments. The results showed that the concentration contained31.11±0.01°Brix soluble solid,17.38±0.23%total sugar, pH3.98±0.01, 2.97±0.22%titratable acid while malic acid was found as the predominant organic acid present in apricot. Total pectin were quantified as3106.35±18.64mg/kg while1587.91±0.87mg/kg of them were soluble. Contents of tannin, ascorbic acid and β-carotene of the concentration were79.69±1.59mg/kg,35.45±0.29mg/100g and35.42±0.53μg/g respectively. The vicosity of the pulp showed as116.95±0.08cP and the volume weighted average particle size (D[4,3]) was134.21±1.89p.m. It was found that the content of pulp in the apricot nectar can be calculated by the determining of buffer coefficient. The correlation equation between pulp content of apricot nectar and its buffer coefficient was established. Meanwhile, the influence of several buffer salts on apricot nectar was investigated. The result showed that the citric acid sodium and sodium tripolyph-osphate buffer systems had a significant effect on the buffer coefficient of the apricot nectar with an almost linear relationship, while the sodium hexametaphosphate buffer system show lower effect and did not exhibit a linear relation.(2) Through central composite design with organoleptic flavour as the evaluation index, the optimum drink formula of apricot nectar was established. The best proportion of ingredients was determined as12%apricot pulp,8.09%sugar and0.10%complex acid. Single factor test and central composite design were carried out to investigate the effect of different stabilizer on the stability of apricot nectar. The mathematical model was established based on3main component indexes selected by factor analysis with sedimentation, absorbance of supernatant, sensory assessment and viscosity as evaluating index. The best formula of the compound stabilizer was optimized as pectin0.35‰, gcllan0.18%‰, and xanthan0.10‰.(3) Non-enzymatic browning in apricot nectar due to entended thermal treatment was investigated. Different indicators were adopted to determine the extent of browning which was found to increase with time and temperature linearly or exponentially. The lightness (L*) and yellowness (b*) fitted well to a first order Kinetic model with activation energy at55.52±4.34kJ/mol and21.62±1.41kJ/mol; The redness (a*) total color difference (△E) and Browning index (A420) fitted well to a zero order Kinetic model with activation energy at31.14±1.17kJ/mol,9.00±0.54kJ/mol and18.35±1.88kJ/mol separately; Accumulation of5-hydroxyl methyl furfural (5-HMF) and degradation of ascorbic acid had good correlation with browning, which can be described by zero and first order kinetic model respectively with activation energy at103.15±2.49kJ/mol and37.32±0.65kJ/mol; Changes of β-carotene such as degradation and isomerism will accelerat the browning with activation energy19.06±0.86kJ/mol. Some useful conclusions were gotten through path coefficient analysis:Oxidation and polymerization of polyphenol and degradation ofβ-carotene were the chief element for deciding browning at60℃; Oxidation of polyphenol and Maillard reaction were the main influence at70℃; Degradation of ascorbic acid was responsible for browning at80℃; Maillard reaction and Oxidation of polyphenol caused browning jointly at90℃and100℃.(4) Color and compound changes of apricot nectar were monitored during storage to gather date of kinetic parameters (rate constant, K and activation energy Ea). The evident increase of the kinetic constants with storage time and temperature can be observed which confirmed that browning is favored by the increase of storage time and temperature. What's more, exposured to natural light would exacerbate the browning. The lightness (L*) and yellowness (b*) fitted well to a first order kinetic model with activation energy at8.50±0.57kJ/mol and28.24±0.87kJ/mol while the redness (a*), total color difference (△E) and Browning index (A420) followed a zero order kinetic model with activation energy being31.14±1.17kJ/mol,27.13±1.68kJ/mol and45.69±2.49kJ/mol respectively; Accumulation of5-hydroxyl methyl furfural (5-HMF) and degradation of ascorbic acid had significant effects on browning, which can be described by zero and first order Kinetic model with activation energy at98.41±1.33kJ/mol and32.03±1.16kJ/mol; Changes of P-carotene accelerated the browning with activation energy at17.93±0.28kJ/mol. Path coefficient analysis showed:Oxidation and polymerization of polyphenol were the chief elements for deciding browning at4℃; Changes of P-carotene and accumulation of5-HMF were the main influences at20℃; A combination of5-HMF, p-carotene and ascorbic acid caused browning when stored at37℃and normal light condition. |
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