果蔬在贮运过程中的生物力学特性及质地检测

为了研究果蔬贮运过程中的品质变化,从力学的角度,讨论了果蔬组织结构与生物力学性质间的关系,分析了果蔬机械损伤特点,介绍了目前果蔬质地力学检测的应用情况和技术概况,总结了该技术目前存在的问题,提出了今后研究的方向和建议。     

Evolution of minor polar compounds and antioxidant capacity during storage of bottled extra virgin olive oil

We characterized "Olivastra Seggianese" extra virgin olive oil (EVOO) and evaluated its chemical and sensory characteristics and antioxidant and antiradical activities during storage under novel conditions. Two oils (A and B) were analyzed for the commodity characteristics at blending (t0) and after 9, 12, and 18 months; panel tests were performed and minor polar compounds (MPC) content was assessed at blending (t0) and after 6, 9, 12, and 18 months. Antioxidant and antiradical activities in vitro were evaluated at t0 and after 12 months, by human low density lipoprotein (LDL) and 1,1-diphenyl-2-picrylhydrazil radical (DPPH*) tests. Oil A, which had an initially higher MPC content, possessed "harder" organoleptic characteristics than oil B, which had a lower MPC content and was endowed with a "smoother" taste profile. Statistical analyses showed that secoiridoids, particularly deacetoxy-oleuropein aglycone, should be quantified to evaluate EVOO stability during storage. The antioxidant activity toward human LDL was linked to MPC content and to storage time. The tests on the stable free radical DPPH* confirmed the results on human LDL. We propose this as an additional parameter to evaluate olive oil quality and stability over time.     

Effect of commercial processing on pesticide residues in selected fruits and vegetables

Commercial food processing operations such as washing, blanching, and cooking remove major portions of the pesticide residues that are currently permitted on the raw agricultural crop. These unit operations are reviewed for selected products, along with degree of residue removal at each step. For example, washing plus peeling removes 99% of carbaryl and malathion residues from tomatoes. Washing removes 83% of benomyl residue from tomatoes and further processing reduces the residue by 98% in tomato puree and catsup. Even in the most concentrated fraction from tomatoes (tomato paste), residues were below the initial level in the raw product.     

Free galactose content in selected fresh fruits and vegetables and soy beverages

The free galactose content was determined in three soy beverages, and 34 selected fruits and vegetables purchased at different times of the year and/or local markets in British Columbia, Canada. The objective of the work was to provide additional information on the free galactose content of foods to assist individuals with galactosemia in making dietary decisions. Free galactose contents in the selected plant materials ranged from 2.0 +/- 0.1 mg/100 g in red potato to 39.7 +/- 1.9 mg/100 g in red pepper. Different time of the season, variety, and storage of the product affected the free galactose contents in most of the plant materials measured in this study. Free galactose levels in kiwi, green seedless grapes, and bell peppers were found to be higher than previous reports, whereas the amount of free galactose in three varieties of tomatoes was significantly lower than previously reported. An evaluation of the change of galactose in Roma tomatoes during ripening showed that free galactose levels increased linearly over time, and storage at 4 degrees C significantly increased free galactose levels in tomatoes. Soy beverages made from soy protein isolate contained less free galactose (1.3 +/- 0.2 mg /100 g) compared to the samples made from whole soybeans (4.8 +/- 1.9 and 5.3 +/- 1.7 mg/ 100 g). This study provides additional information on the range of free galactose in fruits and vegetables which will allow individuals with galactosemia to make more informed dietary choices.     

果蔬气调贮藏冷却阶段温度变化的数值模拟及验证

该文主要针对果蔬的气调贮藏的冷却阶段进行了研究,建立了果蔬气调冷却阶段传热过程数学模型。采用有限差分法,编制了计算程序,对气调库中果蔬的降温进行了数值计算。对果蔬冷却降温过程进行了试验研究,试验结果与编程计算结果吻合较好,模拟温度与试验温度的差值在2℃以内。结果表明,文中的数学模型可以用于预测果蔬在气调冷却过程中的温度变化,这有助于科学地运行制冷设备,同时为气调贮藏果蔬系统的优化设计提供了理论基础。     

果蔬冷库进货期间货物温度稳定性的影响因素

温度是果蔬贮藏环境最重要的参数。为了研究果蔬进库过程中影响货物温度稳定性的因素,该文以西安某苹果冷藏库为研究对象,建立冷库环境三维非稳态数值求解模型,模拟了进货过程中新进货物摆放间距、进货温度和进货量对达到贮藏条件货物温度稳定性的影响。模拟结果表明,在实际运行管理中,存在适宜的进货温度和进货量,可使苹果贮藏环境受进货过程影响最小,进货效率最高;增大进货间距可以减小对货物温度场的影响,进货摆放间距并不是越大越好。该文研究的冷库,进货过程中货物应先预冷到3℃再进库,进货摆放间距为0.5 m,进货量不大于10%。     

Polyphenols and antioxidant capacity of vegetables under fresh and frozen conditions

The phenolic and oxygen radical absorbance capacity (ORAC) values have been measured in six fresh and frozen vegetables (beet green, spinach, broccoli, carrot, onion, and celery) from the same cultivar by analyzing the whole juice (WJ) and the acetonic extract of the squeezed pulp. To exploit the effect of the acid environment on the stability and recovery of the phenolics, perchloric acid (PCA) was added directly to WJ and to the pulp before the extraction with acetone. In both fresh and frozen vegetables, PCA markedly increased the recovery of phenolics extracted from the pulp, but PCA had no effect on the WJ. Four of six frozen vegetables showed lower phenolic and ORAC values than the fresh vegetables, whereas in the other two cases, values were significantly higher compared to fresh samples. Among the fresh vegetables, beet green showed the highest ORAC and phenolic values; however, when measured in two different cultivars of beet green, the ORAC value showed as much as 4.5-fold variation, whereas total phenolics and flavonoids showed 1.2- and 3.5-fold variations, respectively. The results show that total phenolics and ORAC, compared in fresh and frozen vegetables, represent an index of the mildness of blanching in the industry of frozen vegetables and provide a measure of the gap in antioxidants in the diet of people who consume frozen instead of fresh vegetables. The plant genotype is an important source of variability in the ORAC value, which can be conveniently used to increase the intake of antioxidants from vegetables.     

Determination of the total antioxidant activity of fruits and vegetables by a liposome assay

The effects of mixtures of antioxidants on the oxidation of phospholipids have been investigated in large unilamellar liposomes following initiation by 2,2'-azobis(2-aminopropane) dihydrochloride. The lag phase increased linearly with antioxidant concentration. The lag phases of mixtures containing alpha-tocopherol with ascorbic acid showed synergy between the antioxidants, but mixtures of beta-carotene with alpha-tocopherol or ascorbic acid were not synergistic. The liposome system was used to investigate the total antioxidant activity of lipid- and water-soluble extracts from 16 samples of fruits, vegetables, and related food products. The water-soluble extracts caused greater increases in lag phase than the lipid-soluble extracts. The lag phase of liposomes containing the water-soluble extracts from fruits and vegetables increased linearly with the total phenolic concentration, with the continental salad extract having the longest lag phase. The lipid-soluble extract from apples caused the largest increase in lag phase of the lipid-soluble extracts. The lag phases of the lipid-soluble and water-soluble extracts of all fruits and vegetables studied were additive, but no synergy was detected. The lag phase of the liposomes containing both the water-soluble and lipid-soluble extracts varied from 611.5 min for the continental salad extracts to 47.5 min for the cauliflower extracts.     

Phenolic constituents and antioxidant capacity of four underutilized fruits from the Amazon region

The Amazon region comprises a plethora of fruit-bearing species of which a large number are still agriculturally unimportant. Because fruit consumption has been attributed to an enhanced physical well-being, interest in the knowledge of the chemical composition of underexplored exotic fruits has increased during recent years. This paper provides a comprehensive identification of the polyphenolic constituents of four underutilized fruits from the Amazon region by HPLC/DAD-ESI-MS(n). Arac?a? ( Psidium guineense ), jambola?o ( Syzygium cumini ), muruci ( Byrsonima crassifolia ), and cutite ( Pouteria macrophylla ) turned out to be primarily good sources of hydrolyzable tannins and/or flavonols. Additionally, different flavanonols and proanthocyanidins were identified in some fruits. The antioxidant capacity was determined by using the total oxidant scavenging capacity (TOSC) assay. Cutite showed the highest antioxidant capacity followed by jambola?o, arac?a?, and muruci.     

Influence of food acidulants and antioxidant spices on the bioaccessibility of beta-carotene from selected vegetables

Four common food acidulants--amchur, lime, tamarind, and kokum--and two antioxidant spices--turmeric and onion--were examined for their influence on the bioaccessibility of beta-carotene from two fleshy and two leafy vegetables. Amchur and lime generally enhanced the bioaccessibility of beta-carotene from these test vegetables in many instances. Such an improved bioaccessibility was evident in both raw and heat-processed vegetables. The effect of lime juice was generally more pronounced than that of amchur. Turmeric significantly enhanced the bioaccessibility of beta-carotene from all of the vegetables tested, especially when heat-processed. Onion enhanced the bioaccessibility of beta-carotene from pressure-cooked carrot and amaranth leaf and from open-pan-boiled pumpkin and fenugreek leaf. Lime juice and the antioxidant spices turmeric and onion minimized the loss of beta-carotene during heat processing of the vegetables. In the case of antioxidant spices, improved bioaccessibility of beta-carotene from heat-processed vegetables is attributable to their role in minimizing the loss of this provitamin. Lime juice, which enhanced the bioaccessibility of this provitamin from both raw and heat-processed vegetables, probably exerted this effect by some other mechanism in addition to minimizing the loss of beta-carotene. Thus, the presence of food acidulants (lime juice/amchur) and antioxidant spices (turmeric/onion) proved to be advantageous in the context of deriving maximum beta-carotene from the vegetable sources.     

果蔬介电特性研究综述

对食品介电特性的研究,不仅能使人们了解食品的射频或微波特性,研发出最具节能效果的介电加热设备,而且介电特性可用于食品品质的识别。为此,以果蔬为对象,概述了果蔬生物体的介电特性;介绍了测试信号的频率和电压以及环境温度和湿度等测试条件对果蔬介电特性的影响;综述了在果蔬含水率、成熟度、新鲜度、损伤和糖、酸度等品质因素对介电特性影响方面的研究进展;并指出目前研究存在的问题和今后的研究方向。     

Anthocyanin composition of wild Colombian fruits and antioxidant capacity measurement by electron paramagnetic resonance spectroscopy

The qualitative and quantitative anthocyanin composition of four wild tropical fruits from Colombia was studied. Compounds of "mora peque?a" ( Rubus megalococcus Focke.), "uva de árbol" ( Myrciaria aff. cauliflora O. Berg), coral, and motilón ( Hyeronima macrocarpa Mull. Arg.) fruits were separately extracted with methanol-acetic acid (95:5, v/v). The anthocyanin-rich extracts (AREs) were obtained by selective adsorption on Amberlite XAD-7. Each extract was analyzed by HPLC-PDA and HPLC-HRESI-MS(n) with LCMS-IT-TOF equipment in order to characterize the anthocyanin pigments and the coinjection in HPLC using standards allowed identifying the major constituents in each extract. The antioxidant activity was measured by electron paramagnetic resonance (EPR) and UV-vis spectroscopy, using ABTS and DPPH free radicals. The ARE of motilón ( H. macrocarpa Müll. Arg) exhibited the highest radical scavenging activity in comparison to the other extracts. A second-order kinetic model was followed in all of the cases. These results suggested that the studied fruits are promising not only as source of natural pigments but also as antioxidant materials for food industry.     

Olfactory perception of cysteine-S-conjugates from fruits and vegetables

Volatile sulfur compounds have a low odor threshold, and their presence at microgram per kilogram levels in fruits and vegetables influences odor quality. Sensory analysis demonstrates that naturally occurring, odorless cysteine- S-conjugates such as S-( R/ S)-3-(1-hexanol)- l-cysteine in wine, S-(1-propyl)- l-cysteine in onion, and S-(( R/ S)-2-heptyl)- l-cysteine in bell pepper are transformed into volatile thiols in the mouth by microflora. The time delay in smelling these volatile thiols was 20-30 s, and persistent perception of their odor occurred for 3 min. The cysteine- S-conjugates are transformed in free thiol by anaerobes. The mouth acts as a reactor, adding another dimension to odor perception, and saliva modulates flavors by trapping free thiols.     

基于毕渥数的果蔬阶段降湿热风干燥特性

为了揭示阶段降湿热风干燥技术的适用性,该研究在干燥温度60℃、风速1.0 m/s 时,研究了不同厚度胡萝卜片（6、12、18 mm）和龙眼物料在阶段降湿（第1阶段相对湿度（Relative Humidity,RH）50%保持30 min;第2阶段RH 20%至结束）和连续排湿（RH<15%）干燥条件下的干燥特性,传热毕渥数（heat transfer Biot,Bih）和传质毕渥数（mass transfer Biot,Bim）、水分有效扩散系数（effective moisture diffusion coefficient, Deff）、色泽、复水比及能耗值。研究表明：对于厚度为6 mm的胡萝卜片和龙眼物料,相对于阶段降湿,连续排湿有助于提高干燥效率;对于12或18 mm的胡萝卜片,阶段降湿能够提高Deff。6、12和18 mm的胡萝卜片在干燥过程中的Bih分别为0.582 7、1.165 5和1.748 2。6 mm时Bih<1,内部扩散的水分能够及时迁移至表面,维持较低RH有助于加快干燥速率。12或18 mm时Bih>1,物料表面和内部存在着较大的水分和温度梯度,此时需要采用阶段降湿干燥方式。不同厚度胡萝卜片干燥过程中的Bim在0.156 8～0.223 0之间;连续排湿和阶段降湿干燥条件下,龙眼Bim分别为0.110 3和0.084 3。这表明,水分由果肉内部迁移至果肉表面的传质阻力较小,干燥过程中果肉收缩、坚硬的外壳及外界较高RH使得水分迁移产生较大阻力。不同厚度胡萝卜片Bim>0.1,表明物料内部至表面存在较大的水分梯度,应采用高RH以减小表面水分蒸发速率,同时升高物料温度。对于6 mm胡萝卜和龙眼物料,连续排湿干燥条件下色泽较好,复水比高且能耗低;而对于12 或18 mm的胡萝卜片,阶段降湿干燥条件下具有较好的色泽,较高的复水比及较低的能耗。综上,阶段降湿干燥过程中,Bih>1且Bim>0.1时,说明阶段降湿干燥适用于此物料的干燥,否则宜采用连续排湿干燥方式。该研究可为果蔬热风干燥过程中合适的RH调控方式筛选提供理论依据和技术支持。     

Evolution of phenolic compounds and antioxidant activity during malting

Two barley varieties, Gan4 and Hamelin, were malted to investigate the evolution of phenolic compounds and antioxidant activity during malting. The antioxidant activity was evaluated with DPPH radical scavenging activity, ABTS radical cation scavenging activity, reducing power, and metal chelating activity. Results showed that malting had significant influences on individual and total phenolic contents as well as antioxidant activities of two barley varieties. The contents of some phenolic compounds and the antioxidant activities decreased significantly during steeping and the early stages of germination and then increased remarkably during the later stages of germination and subsequent kilning. The most phenolic compounds identified in barley were (+)-catechin and ferulic acid, which both changed significantly during malting. Moreover, results from the Pearson correlation analysis showed that there were good correlations among DPPH radical scavenging activity, ABTS radical cation scavenging activity, reducing power, total phenolic content and sum of individual phenolic contents during malting.     

果蔬热处理传热过程的数值模拟及验证

为了研究果蔬采后热处理过程的传热机理,建立了柱状与球状果蔬热处理的普适传热模型,对模型进行了数值模拟及试验验证。结果表明：所建模型能够准确预测多种边界条件下柱状与球状果蔬热处理时的组织温度变化及动态响应,柱状及球状果蔬的模型预测值与实测值的平均相对误差及均方根误差均低于5%。热水浸泡法与热空气法的对比试验表明：达到相同的热处理效果,伊丽莎白香瓜热水浸泡法的处理时间仅为热空气法的35%～50%;热水浸泡法中香瓜果实的表面换热系数为190～250 W/(m2·℃),而在热空气法中仅为10～30 W/(m2·℃     

Biologically important thiols in various vegetables and fruits

Biological thiols are important antioxidants, and recent studies showed that their contents vary depending on the groups of foodstuffs. Therefore, we investigated the levels of some biological thiols in various vegetables and fruits by using a sensitive high-performance liquid chromatography (HPLC) technique. Biological thiols measured in some vegetables and fruits include glutathione (L-glutamyl-L-cysteinly glycine, GSH), N-acetylcysteine (NAC), captopril [CAP (C9H15NO3S)], homocysteine (HCYS), cysteine (CYS), and gamma-glutamyl cysteine (GGC). Our results show that biological thiol contents are between 3-349 nM/g wet weight in vegetables and 4-136 nM/g wet weight in fruits. CAP is only found in asparagus (28 nM/g wet weight). Furthermore, none of the biological thiols analyzed were found in cabbages, red grapes, blackberries, apples, and peaches. Therefore, various vegetables and fruits differ significantly in their thiol contents. Oxidation of these important thiols may occur and result in the production of toxic byproducts, if they are exposed to radiation and ozone treatment for sterilization purposes. Further studies should be performed to monitor the levels of these biological thiols.     

壳聚糖处理对采后梅杏贮藏品质的影响

为了探讨壳聚糖对采后杏果实贮藏保鲜的作用,以梅杏果实为试材,主要研究了0.75 g/L壳聚糖处理和对照处理对其采后生理和细胞超微结构的影响。结果表明：壳聚糖处理与对照相比,降低了果实的腐烂率,抑制了果实的变软,保持了较高可溶性固形物含量以及较高的过氧化物酶（peroxidase, POD）、超氧化物歧化酶（superoxide dismutase, SOD）、过氧化氢酶（catalase, CAT）等保护酶的活性,而降低了多酚氧化酶（polyphenol oxidase, PPO）的活性和超氧阴离子产生速率。此外,0.75 g/L壳聚糖处理在贮藏过程中可较好地保持梅杏果肉细胞的结构和功能,从而延缓杏果实衰老的进程,为壳聚糖在杏贮藏保鲜中的应用提供参考。