可见光/近红外光谱技术快速测定橙汁柠檬酸含量

为了快速无损测定橙汁的柠檬酸含量,提出了一种用可见光/近红外光谱技术进行检测的新方法。选用高效液相色谱法作为光谱柠檬酸测定的标定方法。采用平滑点数为5的移动平滑法对原始光谱进行预处理消除噪声。由于采集的光谱数据量非常大,为了减少建模时间,建模之前采用小波变换对经过预处理的大量光谱数据进行降维压缩,并在Matlab7.01中通过自编程序实现此变换。利用光谱专用分析软件Unscrambler 9.5,对压缩后的新变量进行分析,建立偏最小二乘(PLS)校正模型。考虑到不同小波基及分解尺度对数据压缩的影响,采用预测平方和PRESS值最小的评价标准,选择最佳的小波基Db4及分解尺度5。用于本实验的样本总数为40,其中30个样本进行建模,10个用于预测。用校正集相关系数(r)和标准偏差(SEC)作为校正模型的评价指标,预测结果采用预测相关系数(r)和预测标准偏差(SEP)来评定。文章将基于小波变换的PLS模型与直接建立的PLS模型进行了比较,偏最小二乘法结合小波变换的模型预测相关系数为r=0.901, 预测标准偏差SEP=0.937;而由PLS建立的模型其预测相关系数r=0.849,预测标准偏差SEP=1.662。由此可见,由偏最小二乘法结合小波变换所得模型效果优于单独使用偏最小二乘法的结果。     

季铵型阳离子蔗渣纤维素对甘蔗清汁的澄清研究

利用新型的季铵型阳离子蔗渣纤维素作为澄清剂,对甘蔗清汁进行吸附脱色研究.本实验在单因素试验结果的基础上,分别选取纯度提高率和色值降低率作为考查指标,利用SPSS软件进行正交试验的设计和数据分析.通过最佳工艺参数的优化试验,得出如下结论:反应温度为80℃、蔗汁中阳离子蔗渣纤维素复合物的加入量为0.4g/100mL甘蔗清汁、接触时间为40min、pH值8.     

高效液相色谱法检测胃液中色氨酸和利多卡因

采用高效液相色谱-紫外-荧光和高效液相色谱-紫外-质谱联用法,证明胃癌患者胃液中存在的荧光物质主要为色氨酸.建立了反相高效液相色谱-双波长同时紫外检测法定量分析胃液中色氨酸和利多卡因的方法.使用Kromasil C18柱(150 mm×4.6 mm, 5 μm),以含0.1%三氟乙酸的甲醇溶液与含0.1%三氟乙酸水溶液为流动相,梯度洗脱分析.色氨酸使用278 nm检测,浓度在0.5～200 mg/L范围内峰面积对浓度的线性相关系数为0.9994;利多卡因使用254 nm检测,浓度在20～5000 mg/L范围内相关系数为0.9992.色氨酸和利多卡因的检出限分别为0.15和5 mg/L;平均加标回收率分别为70.8%～110.4%(色氨酸) 和87.1%～116.2% (利多卡因).利用本方法对38例胃癌患者和48例非胃癌患者的胃液进行测试,两组胃液中色氨酸的含量存在一定的差异.     

HPLC determination of organic acids, sugars, phenolic compositions and antioxidant capacity of orange juice and orange wine made from a Turkish cv. Kozan

Organic acids, sugars, phenolic compositions and antioxidant capacities of orange juice and orange wine obtained from the cv. Kozan of Turkey were determined. High-performance liquid chromatographic methods were used to identify and quantify of these compounds. Three organic acids (citric, malic and ascorbic acids) and three sugars (sucrose, glucose and fructose) were determined. The major organic acid was found as citric acid. With regard to sugars, sucrose was present in the largest amounts for orange juice and wine. A total of 13 phenolic compounds were identified and quantified in orange juice and wine, including hydroxybenzoic acids (2), hydroxycinnamic acids (5), and flavanones (6). Hesperidin, narirutin and ferulic acid were the most abundant phenolic compounds in orange juice and wine. Antioxidant activities of orange juice and wine were measured using the DPPH^• (2,2-diphenyl-1-picrylhydrazyl) assay, and the antioxidant capacity of orange juice was found to be higher than that of orange wine.     

Comparison of extraction methods for volatile compounds of Muscat grape juice

Typical flavour of Muscat d’Alexandrie wines is mainly due to volatile compounds coming from grapes of this variety. Therefore, the choice of grapes is crucial to obtain musts with a great aromatic potential, which will contribute to the final aroma of wines derived from those musts. In this study, three sampling techniques, liquid-liquid extraction (LLE), solid phase extraction (SPE) and simultaneous distillation-extraction (SDE), were compared for the analysis of volatile compounds in Muscat grape juice. Results showed that although the three techniques can be recommended for the quantitative analysis of volatile compounds from musts, LLE and SPE are better sample preparation techniques than SDE, mainly for determination of polar compounds such as acids or alcohols.     

Simultaneous determination of several phytohormones in natural coconut juice by hollow fiber-based liquid–liquid–liquid microextraction-high performance liquid chromatography

A simple, selective, sensitive and inexpensive method of hollow fiber-based liquid–liquid–liquid microextraction (HF-LLLME) combined with high performance liquid chromatography (HPLC)-ultraviolet (UV) detection was developed for the determination of four acidic phytohormones (salicylic acid (SA), indole-3-acetic acid (IAA), (±) abscisic acid (ABA) and (±) jasmonic acid (JA)) in natural coconut juice. To the best of our knowledge, this is the first report on the use of liquid phase microextraction (LPME) as a sample pretreatment technique for the simultaneous analysis of several phytohormones. Using phenetole to fill the pores of hollow fiber as the organic phase, 0.1 mol L⁻¹ NaOH solution in the lumen of hollow fiber as the acceptor phase and 1 mol L⁻¹ HCl as the donor phase, a simultaneous preconcentration of four target phytohormones was realized. The acceptor phase was finally withdrawn into the microsyringe and directly injected into HPLC for the separation and quantification of the target phytohormones. The factors affecting the extraction efficiency of four phytohormones by HF-LLLME were optimized with orthogonal design experiment, and the data was analyzed by Statistical Product and Service Solutions (SPSS) software. Under the optimized conditions, the enrichment factors for SA, IAA, ABA and JA were 243, 215, 52 and 48, with the detection limits (S/N = 3) of 4.6, 1.3, 0.9 ng mL⁻¹ and 8.8 μg mL⁻¹, respectively. The relative standard deviations (RSDs, n = 7) were 7.9, 4.9, 6.8% at 50 ng mL⁻¹ level for SA, IAA, ABA and 8.4% at 500 μg mL⁻¹ for JA, respectively. To evaluate the accuracy of the method, the developed method was applied for the simultaneous analysis of several phytohormones in five natural coconut juice samples, and the recoveries for the spiked samples were in the range of 88.3–119.1%.     

橙汁中多菌灵农药残留吸收光谱特征研究

利用分光光度计,通过对多菌灵及橙汁-多菌灵混合体系的紫外-可见吸收光谱进行研究,得到橙汁中不同农药含量下的吸收光谱特征,分析了吸光度与多菌灵农药含量的关系。研究表明:多菌灵药液在285nm处有较强的特征吸收峰。通过向橙汁中逐量添加0.28mg·mL-1多菌灵标准溶液,与纯多菌灵药液吸收光谱比较,发现峰值位置出现了小幅度蓝移(285~280nm),说明橙汁和多菌灵发生了相互作用,通过对280nm波长处的吸光度与多菌灵药液含量进行最小二乘法线性拟合,建立了橙汁中吸光度与多菌灵农药含量之间的预测模型,发现吸光度与多菌灵药剂含量具有很好的线性关系,其线性函数模型为:I=2.41+9.26x,相关系数为0.996,回收率在81%~102%之间。根据该回归模型,可以得到橙汁中多菌灵农药残留量的准确值,从而验证了利用紫外-可见吸收光谱测定橙汁中多菌灵残留量的方法的可行性。研究表明,利用光谱技术直接对果汁中农药残留检测方法是可行的,能够满足快速分析的需要,本研究为农药残留检测提供了新的途径。     

Thermosonication as a potential quality enhancement technique of apple juice

Enzymatic browning and microbial growth lead to quality losses in apple products. In the present study, fresh apple juice was thermosonicated using ultrasound in-bath (25 kHz, 30 min, 0.06 W cm⁻³) and ultrasound with-probe sonicator (20 kHz, 5 and 10 min, 0.30 W cm⁻³) at 20, 40 and 60 °C for inactivation of enzymes (polyphenolase, peroxidase and pectinmethylesterase) and microflora (total plate count, yeast and mold). Additionally, ascorbic acid, total phenolics, flavonoids, flavonols, pH, titratable acidity, ^°Brix and color values influenced by thermosonication were investigated. The highest inactivation of enzymes was obtained in ultrasound with-probe at 60 °C for 10 min, and the microbial population was completely inactivated at 60 °C. The retention of ascorbic acid, total phenolics, flavonoids and flavonols were significantly higher in ultrasound with-probe than ultrasound in-bath at 60 °C. These results indicated the usefulness of thermosonication for apple juice processing at low temperature, for enhanced inactivation of enzymes and microorganisms.     

Sonication enhances polyphenolic compounds,sugars, carotenoids and mineral elements of apple juice

A study was initiated with the objective of evaluating the effects of sonication treatment on quality characteristics of apple juice such as polyphenolic compounds (chlorogenic acid, caffeic acid, catechin, epicatechin and phloridzin), sugars (fructose, glucose and sucrose), mineral elements (Na, K, Ca, P, Mg, Cu and Zn), total carotenoids, total anthocyanins, viscosity and electrical conductivity. The fresh apple juice samples were sonicated for 0, 30 and 60 min at 20 °C (frequency 25 kHz and amplitude 70%), respectively. As results, the contents of polyphenolic compounds and sugars significantly increased (P < 0.05) but the increases were more pronounced in juice samples sonicated for 30 min whereas, total carotenoids, mineral elements (Na, K and Ca) and viscosity significantly increased (P < 0.05) in samples treated for 60 min sonication. Losses of some mineral elements (P, Mg and Cu) also occurred. Total anthocyanins, Zn and electrical conductivity did not undergo any change in the sonicated samples. Findings of the present study suggest that sonication technique may be applied to improve phytonutrients present naturally in apple juice.     

Preparation of resveratrol-enriched grape juice from ultrasonication treated grape fruits

Grape (Vitis spp.) is a major source of resveratrol that can be eaten directly or after making jam, jelly, wine and juice. Resveratrol (3,5,4′-trihydroxystilbene) has a profound positive influence on human health, including anti-carcinogenic, anti-cancer, anti-inflammatory, and anti-ageing effects and the ability to lower blood sugar. During industrial production of grape juice, resveratrol is lost because of the use of clarifying agents and filtration; therefore, commercial grape juice contains very low amounts of resveratrol. In this study, we investigated the accumulation of resveratrol in grape juice prepared from three varieties of grape, viz. Campbell Early, Muscat Bailey A (MBA) and Kyoho, following post-harvest ultrasonication cleaning for 5 min and 6 h of incubation in the dark at 25 °C. This process resulted in the amounts of resveratrol increasing by 1.53, 1.15 and 1.24 times in juice prepared from Campbell Early, MBA and Kyoho, respectively, without changing the amounts of total soluble solids. Overall, our results indicate that ultrasonication treatment of post-harvested grape fruits can be an effective method for producing resveratrol-enriched grape juice as well as cleaning grapes thoroughly.