NUTRIENT QUALITY OF SELECTED VEGETABLES PREPARED BY CONVENTIONAL AND COOK-FREEZE METHODS

Selected vegetables (spinach, broccoli, sweet potatoes, and collard greens) prepared in 2.27 kg (5 lb) quantities by boiling, were frozen and stored for six months at ?18°C. Zinc, iron, β-carotene, and ascorbic acid were determined on the raw vegetable immediately after cooking and after reheating in a microwave oven subsequent to 6 months frozen storage. The greatest nutrient loss occurred for water soluble nutrients during boiling. Nutrient comparison between cooked samples (conventional method) and samples microwaved after 6 months frozen storage (cook-freeze method) indicated that differences existed only in ascorbic acid content of spinach. Data indicated that vegetables prepared by cook-freeze, a method used by health care institutions, were generally equal in nutrient quality to conventionally prepared vegetables.     

菠菜贮藏过程中水分蒸发损失

研究不同相对湿度对菠菜水分损失的影响。菠菜在贮藏温度5℃、相对湿度99%条件下贮藏44h,不同堆放方式单棵菠菜和捆绑菠菜的失水率分别为41.32%和23.32%;相同温度下,贮藏44h,99%、80%、40%相对湿度条件下,单棵菠菜失水率分别为66.70%、54.60%和41.32%。利用图像处理软件测量得一般市售菠菜的比表面积为48.05cm2/g。建立了菠菜贮藏过程中失水速率和相对湿度的关系,结果表明：储存前期,相对湿度越高,失水速率越慢,随着时间的延长,各相对湿度下的失水速率趋于一致,受相对湿度的影响不大。     

Influence of commercial freezing and storage on vitamin C content of some vegetables

Vitamin C levels of commercially frozen okra, potatoes, green beans, broccoli, spinach and peas, including the impact of processing and storage, were studied. Depending on the vegetable type, prefreezing operations caused a 19.1–51.5% decrease in the initial vitamin C levels. The freezing process alone did not influence the vitamin levels except in the cases of green beans and spinach. Total losses (%) were between 27.6 and 57.9 for the vegetables at the end of commercial frozen storage (6 months). All the data obtained from this study confirmed that, depending on the vegetable type, prefreezing operations have a major impact on the vitamin C contents and this influence persists in the frozen storage.     

The influence of processing and preservation on the retention of health-promoting compounds in broccoli

ABSTRACT:  In this work the effects of common household practices such as chilling, freezing, and cooking on vitamin C retention in broccoli (Marathon cv.), as well as their influence on the release of sulforaphane upon enzymatic hydrolysis of glucoraphanin by the endogenous enzyme myrosinase, were investigated. When chilled at 6 °C and 95% R.H. for 35 d, broccoli showed a vitamin C and sulforaphane loss of about 39% and 29%, respectively, while storage at –18 °C for 60 d resulted in similar losses, but mainly due to the blanching step. Boiling, steaming, microwaving, pressure-cooking, and the combined use of pressure and microwaves were the cooking methods investigated. Boiling and steaming caused significant vitamin C losses, 34% and 22%, respectively, while with the other treatments more than 90% retention was observed. Sulforaphane was no more detectable after boiling or steaming, while pressure/microwave cooking did not cause any significant loss. The quantitative distribution of these moieties in the florets and stems of fresh and chilled broccoli was also investigated.     

西兰花茎提取液对西兰花贮藏品质的影响

为研究营养补偿对西兰花保鲜效果的影响,本试验将西兰花茎通过榨汁制成提取液,通过茎基部浸施方式模拟西兰花生长状态的营养供应,设计了提取液、蒸馏水浸施12 h两个处理,以自然放置为对照,研究了西兰花在10 ℃贮藏期间乙烯释放量、呼吸速率、含水量、失重率、相对电导率和丙二醛（Malondialdehyde,MDA）含量、叶绿素、抗坏血酸（Vitamin C,V_C）、可溶性固形物（Total Soluble Solids,TSS）、可滴定酸（Titratable acid,TA）等指标变化。结果表明,与对照处理相比,提取液处理能够推迟乙烯的释放以及呼吸高峰的到来,降低呼吸强度,乙烯释放及呼吸强度的最大值分别为对照处理的60.29%、77.22%;保持西兰花的含水量,延缓失重,在贮藏末期提取液处理的西兰花含水量达83.64%,失重仅为7.01%;延缓MDA含量和电导率的增加,在贮藏末期提取液处理的MDA含量及相对电导率分别70.19%、49.93%;保持较高的叶绿素含量,达到了7.01 mg/kg;保持较高的V_C含量和TSS含量,比对照处理高出60.99%、20.82%;TA最终含量为0.30%。表明西兰花茎提取液能够对西兰花产生较好的保鲜效果。     

Storage of spinach juice agglomerates: Physical,flow, structural,and thermal properties

The objective of this study was to investigate how the various storage temperatures affected the physical properties, flow characteristics, microstructure, and glass transition temperature of spinach juice agglomerates. For this purpose, spray-dried spinach juice powders were processed to agglomerates by using a modified fluidized bed dryer (1.6 m/s airflow rate, 60°C drying air temperature, 20 min processing time, and with different binder solutions containing agents as maltodextrin, gum Arabic, and whey powder isolate). The analyses were carried out every month throughout 6 months while the spinach juice agglomerates were stored at temperatures of 4, 20, and 35°C. The results revealed that over the storage time, the moisture content and water activity values of the agglomerates were generally under 11% and 0.6, respectively. The color values generally showed a decreasing trend depending on the storage time. The solubility times of the samples stored at 4°C were longer than those of stored at other storage temperatures. The SJA-GA had the lowest HR and CI values and thus the best flowability properties during all storage times. There was no detectable change in the structures of SJA stored at 20°C according to the storage time. Throughout the storage time, it was discovered that the glass transition temperature of all spinach juice agglomerates was remarkably similar. Overall, the investigation revealed that storage at 35°C for 6 months might be suitable because it delivered the intended outcomes such as greater flowability and cohesiveness, and shorter wettability and solubility times.     

Effect of processing and storage of brined white (Nabulsi) cheese on fat and cholesterol oxidation

Brined white (Nabulsi) cheese was studied for cholesterol oxidation and for oxidative and hydrolytic rancidities during cheese processing, during storage in closed transparent and light‐protected glass jars at room temperature for 3, 6 and 9 months and during storage on an open tray exposed to atmospheric air and light for 1, 2 and 3 weeks. The peroxide value (PV), free fatty acid (FFA) content and 7‐ketocholesterol level were determined. The cheese processing steps (curd formation, salting and boiling in brine) had no significant effect on PV, FFAs and 7‐ketocholesterol. However, the storage conditions had a significant effect (p ≤ 0.5) on these parameters. Peroxides were not detected or were very low in the freshly boiled cheese, while the FFA content was 2.9 g kg^?1. The PV and FFA content increased to approximately 5 meq kg^?1 and 11 g kg^?1 respectively after 9 months of storage in transparent or light‐protected jars. The 7‐ketocholesterol level was 1.2 µg g^?1 in the freshly boiled cheese and reached maximum values of 2.3 and 5.2 µg g^?1 after 9 months of storage in light‐protected and transparent jars respectively. Cheese samples displayed on an open tray showed a higher increase in PV, FFAs and 7‐ketocholesterol than samples stored in closed jars, reaching values of 6.1 meq kg^?1, 6.8 g kg^?1 and 8.8 µg g^?1 respectively after 3 weeks of storage. © 2002 Society of Chemical Industry     

光线照射下芫荽和蕹菜常温贮藏效果比较

比较了芫荽(Coriandrum sativum L.)和蕹菜(Ipomoea aquatica Forsk)在20±1℃下光照处理的贮藏效果。在4d贮藏期内,用光合量子通量密度(PPED)为5μmol/m2•s的红光每天连续照射24h。结果表明,与黑暗条件下芫荽和蕹菜贮藏效果相比,光照有利于累积还原糖和减少叶绿素和VC损失,并且光照条件下蕹菜的贮藏效果好于芫荽;贮藏结束时,光照处理的芫荽和蕹菜中叶绿素含量分别比同期黑暗处理的高出76.82%和93.36%,还原糖含量分别高出32.69%和20.57%,VC保存率分别高出2.31和2.38倍;芫荽根部和蕹菜嫩茎切口吸收水分而使其保持鲜嫩状态,两者含水量变化与光照无关。     

Physiology and Quality Responses of Fresh-cut Broccoli Florets Pretreated with Ethanol Vapor

ABSTRACT:  The exposure of intact broccoli to 6 mL/kg ethanol for 5 h was effective in inhibiting the senescence of fresh-cut broccoli florets. During the 8 d of storage at 10 °C, the weight loss, protein, and chlorophyll degradation of the treated broccoli florets were significantly retarded. The ethanol content of the ethanol-treated broccoli rose sharply and then descended rapidly to a level close to that of the control broccoli stored at 10 °C after 8 d. The acetaldehyde level of the treated broccoli was higher than that of the control broccoli over the whole storage period. The alcohol dehydrogenase activity of the treated broccoli was significantly higher than that of the control after 6 d. There had been higher activities of peroxidase, superoxide dismutase, and catalase in ethanol-treated broccoli. Our study showed that the fresh-cut broccoli treated with ethanol maintained better quality during the storage. Ethanol vapor would be commercially a good candidate for extending the shelf-life of fresh-cut broccoli florets and reducing the loss in postharvest.     

Antioxidant activity of ginger extract in sunflower oil

The antioxidant activity of dichloromethane extract from ginger was evaluated during 6 months of storage of refined sunflower oil at 25 and 45 °C. Free fatty acid (FFA) content, peroxide value (POV) and iodine value (IV) were used as criteria to assess ginger extract as an antioxidant. After 6 months of storage at 45 °C, sunflower oil containing 1600 and 2400 ppm ginger extract showed lower FFA contents (0.083 and 0.080%) and POVs (24.5 and 24.0 meq kg^?1) than the control sample (FFA contents 0.380%, POV 198.0 meq kg^?1). Sunflower oil containing 200 ppm butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) showed FFA contents of 0.089 and 0.072% and POVs of 26.5 and 24.7 meq kg^?1 respectively after 6 months of storage at 45 °C. Similarly, after 6 months of storage at 45 °C, IVs of sunflower oil containing 1600 and 2400 ppm ginger extract were 80 and 92 respectively, higher than that of the control sample (53). However, IVs of sunflower oil treated with 200 ppm BHA and BHT were 94 and 96 respectively after 6 months of storage at 45 °C. These results illustrate that ginger extract at various concentrations exhibited very strong antioxidant activity, almost equal to that of synthetic antioxidants (BHA and BHT). Ginger extract also showed good thermal stability and exhibited 85.2% inhibition of peroxidation of linoleic acid when heated at 185 °C for 120 min. Therefore the use of ginger extract in foods is recommended as a natural antioxidant to suppress lipid oxidation. © 2003 Society of Chemical Industry     

不同预冷方式对西兰花货架期品质的影响

本文研究了不同预冷方式对西兰花货架期品质的影响。将三组西兰花分别做如下三种预冷处理:冷库预冷(对照)、冰预冷、冷水预冷。西兰花中心品温度降至(1±1) ℃后,将西兰花从箱中取出后将西兰花放入温度为(20±1) ℃的库中贮藏。取降至(1±1) ℃的西兰花作为初值,之后每24 h取一次样,用于各种指标的测定。测定结果表明:与冷库预冷比较,冰预冷和冷水预冷处理可以有效抑制西兰花黄化,保持西兰花的色泽和良好的感官品质;提高了西兰花V_C含量、叶绿素和硫代葡萄糖苷含量,贮藏至4 d,冰预冷和冷水预冷处理西兰花的V_C含量要比CK处理分别高出15.6%和39.2%,叶绿素含量分别是CK组的1.87倍和2.44倍,硫代葡萄糖苷的含量仍能达到0.71 mg/g;抑制了西兰花电导率和丙二醛(MDA)含量的上升;提高了西兰花抗坏血酸过氧化物酶(APX)、超氧化物岐化酶(CAT)和过氧化物酶(POD)的活性,其中冷水预冷的西兰花POD活性变化最为显著,保持在一个很高的水平,清除了西兰花体内的H₂O₂和过氧化物、促进了抗氧化系统中的物质,增强了西兰花的抗氧化能力。冰预冷和冷水预冷处理可提高西兰花感官品质,延缓西兰花衰老,延长货架期2~3 d。     

Effects of Processing on Zinc Levels in Spinach, Beef, and Potatoes

Spinach, beef, and potatoes were subjected to combinations of cooking, freezing, retorting, and storage and analyzed for total zinc and water soluble zinc, before and after acid-enzyme digestion. Zinc and its complexes that were soluble were membrane filtered to exclude the passage of substances larger than 5,000 daltons. Approximately 30–50% of the total zinc in spinach systems and about 70–100% of the zinc in potato systems was water soluble. Practically none of the endogenous zinc in beef was water soluble. Regardless of processing method, essentially all zinc in spinach and potatoes and about half of the zinc in beef was released after acid-enzyme digestion. All of the spinach and potato zinc and at least a third of the beef zinc following digestion passed through the 5,000 dalton membrane.     

β-Carotene and Ascorbic Acid Retention in Fresh and Processed Vegetables

Broccoli, carrots, and green beans (grown in 2 consecutive years) were randomly divided into 3 treatments: fresh-refrigerated (F-R), frozen (FZ) or canned (C) (carrots only). FZ or C vegetables were processed within 24 h and stored for up to 1 yr. F-R vegetables were held at 4 °C for 3 wk (broccoli and green beans) or 6 mo (carrots). Trans b-carotene (Tb-C) and total ascorbic acid (AA) were determined at specified times, before and after microwave cooking. Vitamin content differed between years due to environmental conditions. Blanching resulted in AA loss, but retention remained stable after freezing broccoli and green beans. F-R green beans lost >90% AA after 16 d storage. Linear decreases in AAwere found in most F-R or FZ vegetables. Tb-C decreased slightly during freezer storage. Reductions in Tb-C occurred in canned carrots. Microwave cooking had minimal effects on AA or Tb-C.     

Retention of Folate, Carotenoids, and Other Quality Characteristics in Commercially Packaged Fresh Spinach

ABSTRACT: The effect of storage temperature (4 °C, 10 °C, and 20 °C) on retention of folate, carotenoids, and other quality characteristics in commercially packaged fresh spinach were determined. Based on visual color and appearance, spinach was unacceptable after 8 d, 6 d, and 4 d at 4 °C, 10 °C, and 20 °C, respectively. Color differences (AE), chlorophyll degradation, fresh weight loss, and microbial populations increased at all storage temperatures and occurred more rapidly at higher temperatures. Peroxidase activity increased but was not significantly ( P > 0.05) affected by storage temperature. Lipoxygenase activity was unaffected by storage time or temperature. Substantial losses of nutrients occurred at each storage temperature. Only 53% of folate in packaged spinach was retained after 8 d, 6 d, and 4 d at 4 °C, 10 °C, and 20 °C, respectively. Carotenoid losses increased with temperature with only 54%, 61%, and 44%, respectively, of initial detected levels remaining. Vitamin and quality changes were unaffected by presence or absence of packaging.     

Effects of the methods of pre-treatment before freezing on the retention of chlorophylls in frozen leaf vegetables prepared for consumption

The investigation included kale, New Zealand spinach and spinach. The evaluation covered the raw material; the raw material after blanching; the raw material after cooking; and frozen products prepared for consumption after 0, 4, 8 and 12 months of refrigerated storage. Both the traditional method of freezing (blanching before freezing) and the modified method of freezing (cooked before freezing) were used in the experiment, as well as two storage temperatures, T = −20 °C and T = −30 °C. The content of chlorophylls in fresh kale was four times that in New Zealand spinach and 1.5 times that in spinach. With the exception of New Zealand spinach, blanching and cooking significantly reduced the content of chlorophylls. In kale products prepared for consumption, the content of chlorophylls decreased in each successive stage of the investigation. In products of New Zealand spinach and spinach, the losses were usually not significant. After 12 months of refrigerated storage, frozen kale products prepared for consumption retained 52–65% of total chlorophylls compared with the content in the raw material; products of New Zealand spinach and spinach retained 66–71%. In kale and New Zealand spinach, the content of chlorophyll a decreased more rapidly than that of chlorophyll b, while in spinach the converse was true. The kale products obtained using the modified method contained more chlorophylls, while in the two spinach species their content was lower. The lower storage temperature resulted in a higher retention of chlorophylls in vegetables.     

A comparison of the vitamin C content of fresh and frozen vegetables

This study, using vitamin C (ascorbic acid) as ‘marker’, allowed a direct comparison of the nutritional quality of fresh vegetables at various stages of distribution and storage, with the same vegetable commercially quick-frozen and stored deep frozen for up to 12 months. The nutrient status of frozen peas and broccoli was similar to that of the typical market-purchased vegetable and was superior to peas that have been stored in-home for several days. Fresh peas and broccoli retained their quality for up to 14 days when stored under chill conditions. The nutrient status of frozen whole green beans and frozen carrots, with no loss on freezing, was similar to the fresh vegetable at harvest. Frozen spinach also compared reasonably well with the harvested fresh vegetable and was clearly superior to all market produce.     

THE INFLUENCE OF POSTHARVEST STORAGE, TEMPERATURE AND DURATION ON QUALITY OF COOKED BROCCOLI FLORETS

Fresh broccoli heads (Brassica oleracea L. var, italica) were stored at 1C, 5C or 10C from 0 to 14 days. After this postharvest treatment, heads were cut into florets, which were given a short heat treatment and afterwards stored in plastic bags for a period of 8 days. Storage time and storage temperature before processing affected the texture and color, chlorophyll, vitamin C and β-carotene of cooked florets. The texture of cooked florets was highly correlated with water loss of the raw heads. Significant correlations were found between yellowness, instrumental color measurements and chlorophyll for cooked broccoli. Vitamin C content was affected significantly by subsequent chill temperature storage of cooked florets, which previously were stored at 5C for a period from 0 to 14 days. After 3 or 8 days of subsequent chill temperature storage of cooked broccoli florets, the vitamin C content seemed to reach almost the same level irrespective of the duration of storage of the raw heads, β-carotene content of cooked broccoli florets was stable when raw broccoli heads were stored at 1C and 5C, whereas it decreased towards the end of the storage period when the heads were stored at 10C. After cooking, β-carotene content remained stable during subsequent chill temperature storage.     

Modifying the Processing and Handling of Frozen Broccoli for Increased Sulforaphane Formation

Frozen broccoli can provide a cheaper product, with a longer shelf life and less preparation time than fresh broccoli. We previously showed that several commercially available frozen broccoli products do not retain the ability to generate the cancer‐preventative agent sulforaphane. We hypothesized that this was because the necessary hydrolyzing enzyme myrosinase was destroyed during blanching, as part of the processing that frozen broccoli undergoes. This study was carried out to determine a way to overcome loss of hydrolyzing activity. Industrial blanching usually aims to inactivate peroxidase, although lipoxygenase plays a greater role in product degradation during frozen storage of broccoli. Blanching at 86 °C or higher inactivated peroxidase, lipoxygenase, and myrosinase. Blanching at 76 °C inactivated 92% of lipoxygenase activity, whereas there was only an 18% loss in myrosinase‐dependent sulforaphane formation. We considered that thawing frozen broccoli might disrupt membrane integrity, allowing myrosinase and glucoraphanin to come into contact. Thawing frozen broccoli for 9 h did not support sulforaphane formation unless an exogenous source of myrosinase was added. Thermal stability studies showed that broccoli root, as a source of myrosinase, was not more heat stable than broccoli floret. Daikon radish root supported some sulforaphane formation even when heated at 125 °C for 10 min, a time and temperature comparable to or greater than microwave cooking. Daikon radish (0.25%) added to frozen broccoli that was then allowed to thaw supported sulforaphane formation without any visual alteration to that of untreated broccoli.