| During processing of kiwi juice, browning and astringency are the main technical problems that obsess juice-processing enterprises. Large amounts of polyphenol came from the non-commercial and hard kiwifruit is squeezed into kiwifruit juice. This is the main reason of browning and astringency of kiwi juice during processing. Browning and astringency become the key point for the development of kiwi juice industry. In addition, pomace, as the by-product of kiwi juice processing, is also rich in polyphenols. Therefore, extracting and recycling of polyphenols can not only improve the production efficiency of kiwi processing, but also produce high value anti-oxidative polyphenols products.First of all, two kinds of macroporous adsorption resin were compared. The optimal one was selected by the absorption properties of polyphenols in kiwi fruit juice. The absorption properties, absorption isotherm, thermodynamic properties and absorption kinetics of the resin were also determined. Dynamic absorption and desorption of the resin of polyphenols were studied in kiwi fruit juice. The optimal condition was decided. The analyzing and identifying methods were also investigated of the separated polyphenols. Composition of polyphenols in kiwi pomace was analyzed by HPLC-MS/MS. The effect factors on the extraction of individual polyphenols by ultra-sound were investigated by the design of Plackett Burman test. The optimal extraction conditions and model were established using Response surface methodology to predict the extraction results. Finally, based on Fick’s second law, kinetic equations of ultrasound-assisted extraction were derived. Kinetic model of ultrasound-assisted extraction of kiwi pomace was eventually established. The main contents and results are as follows:(1) By comparison of adsorption performance of in kiwi fruit juice of two kinds of macroporous adsorption resin, it was found that AB-8 resin showed better adsorption properties. The static adsorption amount of polyphenols of AB-8 was up to 31.304 mg/g. The AB-8 resin adsorption isothermal of polyphenols in kiwi fruit juice was consistent with the Freundlich equation. Thermodynamic studies proved that it belonged to physical adsorption and the endothermic process due to enthalpy variables (0< △H< 5). As temperature increasing, free energy (△G< 0) showed a trend of decline, suggesting that the process of adsorption was spontaneous adsorption. Dynamics study confirmed that Lagergren pseudo-first-order equation can well match the adsorption process of polyphenols in kiwi fruit juice by AB-8 resin. Adsorption mechanism showed that inner diffusion process was not the speed limiting step, and the whole process was limited by liquid film diffusion and inner adsorption process at the same time.(2) In order to remove and recycle polyphenols in kiwi juice continuously, optimization research of the conditions that AB-8 resin adsorbing and desorbing polyphenols in kiwi juice was carried out by response surface methodology. Subsequently, the composition of polyphenols isolated from kiwi juice was analyzed. The dynamic adsorption predictive model was Yi=-18.19+6.71 X1+0.84 X2+2.65 X3-0.1 X1X2-0.05 X1 X3-0.028 X2X3-1.69 X12 -0.014 X22-0.152 X32. The model had good reproducibility, with R2=0.975, P<0.01. The dynamic desorption predictive model was Y2= 162.73+4.29A+64.81B+60.18C+0.27,AB-0.48 AC-4.05 BC -0.039A2-14.3932-5.14C2. The model was good at reproducibility, with R2=0.965, P<0.01.The optimal dynamic adsorption conditions were as follows:kiwi juice concentration 19 °Brix, the sample flow rate of 1.3 mL/min, the injection volume 7 BV. The dynamic desorption conditions were 45% ethanol, the flow rate of parsing 2.4 mL/min, desorption capacity of ethanol 3 BV. The resin eluate was detected and eight kinds of polyphenols monomer were detected. Rutin had the highest concentration of 2.68μg/mL, followed by epicatechin 1.357μg/mL. Validation test showed that the dynamic adsorption capacity was 3.16 mg/g resin and the Dynamic desorption rate was 91.75%. The result of the test was very close to the predicted values. Hence, the predicted model meets the test requirements.(3) The composition of polyphenols of kiwi pomace was investigated by the mass spectrometric analysis. Based on single factor tests, Box -Behnken experimental design was used for the optimization of ultrasonic extraction of polyphenol.13 different phenols in kiwi pomace were detected and identified using LC/MS method. They were protocatechuic acid, chlorogenic acid, catechinic acid, vanillic acid, caffeic acid, syringic acid, epicatechin, ferulic acid, rutin, hyperin, isoquercitrin, quercitrin and quercetin. Plackett Burman design was applied to study the effect of factors on ultrasonic extraction. The significant factors were power, frequency arid temperature. The effects of ultrasonic power, frequency, temperature and the ratio of solvent to pomace on the extraction of polyphenols were evaluated. Ultrasonic power exerted great effect on polyphenol acid, little effect on flavones. More polyphenols acid and flavones were extracted under low frequency. More polyphenol acid were extracted under low temperature, however more flavones under high temperature. More polyphenols was extracted under high ratio of solvent to pomace. The prediction model was Yi=24.18+1.01 X1+1.56 X2+0.69 X3+0.11 X1 X2-0.062 X1 X3-0.067 X2 X3-1.59 X1-2.31 X22-1.06 X32. The model showed good reproducibility as its coefficient of determination R2=0.972 and P<0.01. According to this model, optimal extraction conditions were ultrasonic power 490W, extraction temperature 66℃ and solid-to-liquid ratio 1:7.5 (w/v). Under such extraction conditions, the experimental yield of polyphenols was up to 26.03 mg/g which was close to the predicted value.(4) The kinetic equation of ultrasonic assisted extraction of polyphenols from kiwi pomace was established using ultrasonic power, ultrasonic frequency, temperature as parameters. The relationship between conventional extraction diffusion coefficient k and temperature was:k=-4 ×10-6T2+0.0004T+0.008, R2=0.936. The relationship between the correlation coefficient kp and power was:kp=2×10-6P-0.0004; the relationship between the correlation coefficient kf and ultrasonic frequency was:kf=-8×10-6f2+ 0.0011 f-0.0211; the relationship between the correlation coefficient kT and temperature was:kT=6×10-6T2 -0.0007 T+0.0185.The interaction coefficient k4 of temperature, ultrasonic power and frequency was 0.80.The kinetics equation of ultrasonic assisted extraction of polyphenols from kiwi fruit peel: In[(18.31+e0.00687)/(18.31+e0.0068T)C]=(-4×10-6T2+0.004T+o.008)[1+0.8[(6×10-6T2-0.00.7T+0.0185)T +(2×10-6P-0.0004)P+(-8×10-6f2+0.0011f-0.0211)f)]tThrough verification test,the fit bet’ween experimental and model calculated values was high,with a correlation coefficient greater than 0.99.The results showed that the model could be used to describe the extraction process of polyphenols from kiwi pomace. |
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