Retention of Phytochemicals in Fresh and Processed Broccoli

Our objective was to determine whether steam blanching, storage and preparation affected concentrations of sulforaphane (SF), sulforaphane nitrile (SFN), cyanohydroxybutene (CHB), iberin (I) or iberin nitrile (IN) in fresh and frozen broccoli. Broccoli (var. “Arcadia”) was grown in St. Charles, IL over three seasons. Samples were steam blanched (2 min at 93 ± 5°C) within 24h of harvest, frozen and stored at ?20°C up to 90 days, and fresh broccoli was stored at 4°C up to 21 days. Samples were analyzed uncooked or microwave cooked. SF, SFN, I, IN and CHB were determined by GC in dichloromethane extracts from lyophilized samples. Rates of loss for CHB and SF were similar during storage of fresh broccoli. Blanching, storage, and microwave cooking decreased (p < 0.01) concentrations of each compound in fresh and frozen broccoli.     

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.     

Irradiation temperature influences product quality factors of frozen vegetables and radiation sensitivity of inoculated Listeria monocytogenes

Four frozen vegetables (broccoli, corn, lima beans, and peas) were gamma irradiated at subfreezing temperatures ranging from -5 to -20 degrees C to determine (i) the radiation sensitivity of an inoculated outbreak strain of Listeria monocytogenes (ATCC 49594), (ii) the effect of changing irradiation conditions (i.e., temperature) on that sensitivity, and (iii) the effect of the recommended radiation dose on the texture and color of irradiated frozen vegetables. The amounts of radiation necessary to reduce the bacterial population by 90% (D10-values) for L. monocytogenes differed significantly among vegetables at each irradiation temperature. D10 increased significantly with decreasing temperature for all vegetables, with each vegetable showing a different response pattern. At an irradiation temperature of -5 degrees C, D10 ranged from 0.505 kGy for broccoli to 0.613 kGy for corn. At -20 degrees C, D10 ranged from 0.767 kGy for lima beans to 0.916 kGy for peas. At -20 degrees C, radiation doses sufficient to achieve a 5-log10 kill (3.9 to 4.6 kGy) caused significant softening of peas and broccoli stems but not of corn or lima beans. Lower doses of comparable antimicrobial efficacy delivered at -5 degrees C (2.5 to 3.1 kGy) did not cause significant changes in texture in any vegetable. Color varied significantly among the dose-temperature combinations only for broccoli florets; this variation did not demonstrate a clear pattern of quality changes in response to irradiation.     

VITAMIN C AND β-CAROTENE IN FRESH AND FROZEN GREEN BEANS AND BROCCOLI IN A SIMULATED SYSTEM

The reduced ascorbic acid and β-carotene contents of “retail market-fresh” (RMF) and “fresh-frozen” (FF) green beans and broccoli in a simulated handling system were determined. Changes in ascorbic acid content in the two vegetables during a retail market period and frozen storage followed different patterns. In green beans, ascorbic acid content decreased during refrigerated storage for up to 7 days, but in broccoli there was a significant increase. Blanching resulted in a loss of approximately 40% of the ascorbic acid in broccoli. Ascorbic acid content of FF green beans stored at-20C for 16 weeks was approximately twice that in RMF green beans, but in FF broccoli stored under the same conditions it was only about half that of RMF broccoli. β-carotene content of green beans and broccoli did not change during either the retail market simulation of frozen storage and did not differ from that of fresh.     

Influence of yeast and vegetable shortening on physical and textural parameters of frozen part baked French bread

The objective of this project was to study the influence of yeast and vegetable shortening on physical and textural parameters of frozen part baked French bread stored for 28 days and to produce a frozen part baked bread with physical and textural characteristics similar to those of the fresh one. Four formulations were used with different quantities of yeast and vegetable shortening. Dough was prepared by mixing all ingredients in a dough mixer at two speeds. After resting, the dough was divided into 60 g pieces, molded and proofed. The bread was partially baked for 7 min at 250°C, in a turbo oven. After cooling, it was frozen until the core temperature reached −18°C and stored at the same temperature up to 28 days. Once a week, samples were removed from the freezer to complete the baking process, without previous thawing. Mass, volume, water content, firmness, cohesiveness and springiness were measured 1 h after final baking. Resistance to extension and extensibility of dough were measured after mixing. Specific volume and chewiness were determined. Bread with higher yeast content presented a higher specific volume, whereas vegetable shortening reduced its crumb firmness and chewiness.     

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.     

Pectin Methyl Esterase Activity in Southern Peas (Vigna sinensis)

SUMMARY: Pectin methyl esterase (PME) activity was investigated in vitro in Southern peas (Vigna sinensis). Experiments were conducted to determine the effect of NaCl concentration, pH, temperature, maturity, frozen storage and rinsing the peas on PME activity.
The optimum salt level for maximum PME activity in the Purple Hull Pink Eye (PHPE) and Princess Ann (PA) varieties was ascertained to be 0.25 M. The pH optima were: PHPE, 8.5; and PA, 7.5 to 8. The remaining studies were made using peas of the PHPE variety which were harvested at 3 stages of maturity. Maximum enzymatic activity occurred at 50°–60°C. Partial inactivation occurred at 65°C. The mean Q₁₀ was 1.35 over the range of 30°–50°C.
PME activity was dependent upon the maturity of the peas. The most immature peas had an activity level about 2.5 times that found in the most mature peas. Peas subjected to frozen storage had a higher activity than the fresh peas; the increased activity was more pronounced in the more mature peas.
Rinsing the peas removed significant amounts of the enzyme. A greater proportion of PME was removed from the more immature peas than from the more mature ones. With the immature, frozen peas PME activity was reduced 22.7% by rinsing; whereas, in the fresh counterpart the reduction was 11.1%. The rinse water from frozen peas contained more PME activity than did rinse water from fresh peas. Also, the activity in rinse water from the most immature peas was about 2.7 times that from the most mature ones. Upon standing, PME activity in the slurries prepared from frozen peas continued to increase up to 3–4 hr.     

Quality changes in soup from deboned chicken frames at refrigerated (4 ± 1 °C) and frozen (−18 ± 1 °C) storage

Chicken soup was made from the broth collected after the pressure cooking of deboned chicken frames (bones). The quality of stored chicken soup (S1) was compared with the soup prepared from the stored chicken broth (S2) at refrigerated (4 ± 1 °C) and frozen (−18 ± 1 °C) storage up to 12 and 90 days, respectively. Thiobarbituric acid reactive substances values and microbial counts were significantly ( P  < 0.01) higher in stored soup (S1) compared with fresh soup (S2). Psychrotrophs and coliforms were not detected. Appearance and odour scores of broth were satisfactory throughout the storage. Sensory attributes were rated better for fresh soup (S2) made from stored broth than stored soup (S1) but all the attributes were decreased with increasing storage period. The stored soup was acceptable up to 9 and 90 days in refrigeration and frozen storage respectively, while the soup made from refrigerated stored broth was acceptable for 12 days.     

Growth and germination of proteolytic Clostridium botulinum in vegetable-based media

The growth of proteolytic Clostridium botulinum from spore inocula and changes in spore counts in mushroom, broccoli, and potato purées were monitored. Four strains of proteolytic C. botulinum types A and B were inoculated separately at approximately 10(4) spores per ml in nutrient broth and vegetable purées incubated at 15, 20, and 30 degrees C for up to 52 days. The times for the cell populations to increase 1,000-fold (T1,000) in the tested vegetables (1 to 5 days at 30 degrees C, 3 to 16 days at 20 degrees C, 7 to > 52 days at 15 degrees C) were similar to those for meat or fish. Only temperature significantly influenced growth rate. In contrast, the lag phase depended on the strains and media tested, in addition to temperature. Lag times and T1,000S for proteolytic C. botulinum were longer for potato and broccoli purées than for mushroom purée. These differences were not related to different pHs or redox potentials. The germination level, evaluated as the decrease in the spore count, was low. The addition of a germinant mixture (L-cysteine, L-alanine, and sodium lactate) to some strains inoculated in vegetable purées resulted in an increase in germination, suggesting a lack of germination-triggering agents in the vegetable purées.     

Influence of vegetable shortening and emulsifiers on the unfrozen water content and textural properties of frozen French bread dough

The influence of vegetable shortening (VS) and emulsifiers (calcium stearoyl-2-lactylate (CSL) and polysorbate 80 (PS80)) on frozen French bread dough has been studied. Eight formulations without yeast were used with different quantities of VS, CSL and PS80. Dough was prepared by mixing all ingredients in a dough mixer at two speeds. The fresh dough was divided into 60 g pieces and molded. Fresh dough samples were also collected for water content and textural analyses. The dough pieces were packed, frozen in a freezer at −30°C and stored at −18°C up to 56 days. After 2, 7, 21, 28 and 56 days of frozen storage, samples were removed from the freezer, thawed at ambient temperature and textural analyses were conducted.The enthalpy of freezable water on fresh bread dough was determined by Differential Scanning Calorimetry (DSC) at the heating rate of 3°C/min, temperature range of −40°C to 20°C. The value of unfrozen water was 0.30–0.34 g H₂O/g solids and additives used during the storage up to 56 days significantly affected the textural properties of frozen dough.     

Evaluation of a select strain of Lactobacillus delbrueckii subsp. lactis as a biological control agent for pathogens on fresh-cut vegetables stored at 7 degrees C

Raw vegetables inoculated with selected pathogenic bacteria were treated with a strain of Lactobacillus delbrueckii subsp. lactis, which was selected for its ability to produce hydrogen peroxide at refrigerated temperatures. The vegetables inoculated included broccoli, cabbage, carrots, and lettuce. Each vegetable was rinsed, chopped, and stored under conditions similar to those used for ready-to-eat vegetables sold at retail. Portions of each vegetable were separately inoculated with one of two pathogenic bacteria, Escherichia coli O157:H7 or Listeria monocytogenes. Prior to packaging, one portion of each inoculated vegetable was treated with a cell suspension of the selected strain of L. delbrueckii subsp. lactis. The vegetables were stored at 7 degrees C for 6 days. The populations of pathogens and lactobacilli on each sample were enumerated on storage days 0, 3, and 6. Although populations of L. delbrueckii subsp. lactis remained at high levels during storage, there was no noticeable antagonistic action against the pathogens under conditions similar to those used for these products at the retail level. Each pathogen survived on all vegetables throughout storage. Further testing revealed that there was apparently sufficient catalase activity in the cut vegetables to destroy enough of the hydrogen peroxide to prevent antagonistic action against the pathogens.     

Influence of the glass transition and storage temperature of frozen peas on the loss of quality attributes

Green peas of two different maturities were used to evaluate the influence of the glass transition temperature (Tg′) and storage temperatures on quality loss during frozen storage. Young peas which have a lower tenderness rating (TR) value, possibly with less starch and higher sugar content than old peas, gave a lower Tg′ value. Quality attributes, including green colour and vitamin C, were measured over time when the peas were stored at ?5, ?12, ?20, ?25 and ?30 °C, respectively. The results indicated that these qualities were maintained during frozen storage as long as the peas remained below or close to their Tg′. The loss of quality at different storage temperatures is relative to the difference between the storage temperature and the Tg′, where the bigger the difference, the greater the loss.     

Microbiological quality and production of botulinal toxin in film-packaged broccoli, carrots, and green beans.

The production of toxin by a 10-strain mixture of proteolytic Clostridium botulinum in fresh produce packaged in polyethylene films with different oxygen permeability was determined. Broccoli florets, shredded carrots, and green beans inoculated with approximately 10(2) C. botulinum spores per g were placed in bags (1.4 kg per bag) composed of four films with different oxygen transmission rates (OTRs). Broccoli was packaged in bags with OTRs of 3 (7,000 cm3/m2/24 h) and 4 (16,000 cm3/m2/24 h), and green beans were packaged in bags with OTRs of 2 (6,000 cm3/m2/24 h) and 4. Broccoli and green beans in bags were compressed and heat-sealed. Shredded carrots were packaged in bags with OTRs of 1 (3,000 cm3/m2/24 h) and 3 and vacuum-sealed. Produce was stored at 4, 13, and 21 degrees C for up to 27 (broccoli) or 28 (carrots and green bean) days and analyzed periodically. At each sampling time, gas composition within the bags, pH of the produce microbial population (total aerobic and anaerobic microorganisms, lactic acid bacteria, psychrotrophic bacteria, yeasts, and molds), and the presence or absence of botulinal toxin were determined. Packaging material affected the quality of vegetables, especially broccoli stored at 4 and 13 degrees C. For example, broccoli was scored as "good" after 22 days at 4 degrees C when it was packaged in film with higher gas permeability (OTR of 4), whereas broccoli appeared to be in "poor" condition when packaged in film with lower gas permeability (OTR of 3). With the exception of lactic acid bacteria, packaging material did not noticeably influence the growth of microorganisms. Lactic acid bacteria grew better in broccoli packaged in bags with an OTR of 3 than in those with an OTR of 4 at all temperatures. Botulinal toxin was detected in broccoli packaged in bags with an OTR of 3 and stored at 13 degrees C for 21 days and in those with an OTR of 4 and 3 and stored at 21 degrees C for 10 days. All toxic samples were visibly spoiled. Toxin was not detected in produce packaged under any other test conditions.     

Effects of cooking methods on chlorophylls, pheophytins and colour of selected green vegetables

The effect of microwave and conventional cooking methods on chlorophyll pigments and colour properties of squash, green beans, peas, leek, broccoli and spinach were studied, by HPLC and colorimetry, respectively. In five of six vegetables, chlorophyll a was found more heat resistant compared with chlorophyll b, except in peas. Chlorophylls in peas were retained to the 80–90%, the highest in all vegetables evaluated. Chlorophylls were retained to 19–100%, depending on the vegetable type and cooking method. Pheophytins increased in all vegetables after cooking. Highest chlorophyll a and chlorophyll b losses were observed in boiled leek while microwaved peas and boiled peas retained the most chlorophyll a and chlorophyll b, respectively. Pheophytin a and pheophytin b formation was highest at boiled squash and boiled green beans, which were fifty‐ninefold and twenty‐onefold compared with fresh ones, respectively. Most of the pheophytin formations occurred in boiled and the least in microwaved vegetables. Surface colour changed depending on the type of vegetable and cooking method.     

Effect of preliminary and culinary processing on amino acid content and protein quality in frozen French beans

The aim of the study was to evaluate the content of amino acids and protein quality of French bean pods. The investigated material consisted of the raw vegetable, fresh pods cooked to consumption consistency, and two kinds of frozen products stored for 12 months at ?20 °C and then prepared for consumption: frozen beans obtained using the traditional method (blanching before freezing) and frozen products of the ready‐to‐eat type (cooking before freezing). A comparison of the amino acid content in the product prepared for consumption showed that the lowest quantities were found in French beans obtained using the traditional method; products obtained using the modified technology and beans cooked directly after harvest had similar levels of most amino acids. The content of amino acids in 16 g N was less varied than in 100 g of the product. The protein in all the three products prepared for consumption as well as that in fresh bean pods hardly differs, as confirmed by the values in the essential amino acid index (EAA). The first limiting amino acid was methionine with cystine and the second was lysine.     

液氮/液氨速冻鮰鱼片理化性质与组织结构变化

研究分析液氮与液氨速冻对斑点叉尾鮰鱼肉品质的影响。新鲜斑点叉尾鮰分割鱼片后分别进行工业隧道式液氮喷淋速冻（－90 ℃、35 min）、隧道式液氨速冻（－35 ℃、90 min）,速冻样品置于－18 ℃下贮藏90 d。分析比较新鲜鱼肉以及速冻鱼肉在不同冻藏时间解冻损失率、蒸煮损失率、加压失水率、剪切力、pH值、K值、挥发性盐基氮（total volatile basic nitrogen,TVB-N）含量、三甲胺（trimethylamine,TMA）含量与硫代巴比妥酸反应物（thiobarbituric acid reactive substance,TBARs）值,应用荧光显微镜观察鱼肉组织微观结构变化。结果表明：与新鲜鱼肉相比,速冻鱼肉蒸煮损失率增加,加压失水率、剪切力、pH值降低,K值、TVB-N含量、TMA含量、TBARs值均呈上升趋势;随着冻藏时间延长,速冻鱼肉理化性质发生劣变;鱼肉速冻后肌肉细胞面积减小,细胞间隙增大;相比液氨速冻,液氮速冻更有利于保持鱼肉持水性、新鲜度以及组织结构完整性,可有效抑制鱼肉冻藏期间的品质劣变。综上,液氮速冻可以有效保持冷冻鱼肉品质,冻藏30 d内,液氮速冻鱼肉品质特性更接近于新鲜鱼肉。     

Effect of hydrothermal treatment on the antioxidant properties of broccoli (Brassica oleracea var. botrytis italica) florets

In the extracts of fresh raw and frozen broccoli, caffeic, ferulic, sinapinic acids and kaempferol were identified. Boiling reduced the amounts of caffeic acid and kaempferol in both samples. The concentration of polyphenols was 2.69 mg/g fresh mass and 0.96 mg/fresh mass in fresh raw broccoli and frozen raw broccoli, respectively. Boiling significantly decreased the amounts of phenolic compounds in fresh broccoli (1.58 mg/g of fresh mass). In the case of frozen broccoli, boiling increased the concentration of polyphenols by 38%. Fresh broccoli extract neutralized free radicals by 19.87%. Boiling significantly reduced its antiradical activity (to 15.06%). Samples of frozen broccoli had a 27.06% antiradical ability. Boiling did not change the antiradical activity in frozen broccoli case. Hydrothermal processing significantly influenced on the ability of the extracts to inhibit the decolorization of β-carotene emulsion. The extract of fresh broccoli had a higher activity when uncooked. Boiling seemed to increase this activity in the case of frozen broccoli samples. The results of the studies on the ability of broccoli extracts to inhibit linoleic acid autooxidation were ambiguous and depended on the method applied. No correlation was found between the content of phenolic compounds and the antioxidant activity of the extracts, regardless of the experimental variant and technique used.     

The antioxidant activity and composition of fresh, frozen, jarred and canned vegetables

Regular consumption of dietary antioxidants may reduce the risk of several serious diseases. As vegetables are a major source of antioxidants it is desirable to assess their antioxidant activity and compare different processing and preparation methods. The total antioxidant activity was determined in water- and lipid-soluble extracts from fresh, stored and frozen vegetables. The contribution of individual compounds to total antioxidant activity was estimated. In stored vegetables at ambient or chill temperatures antioxidant activity declined. Blanching and freezing of peas and spinach reduced water-soluble antioxidant activity by 30 and 50%, respectively, thereafter levels remained constant on storage at −20 °C. Samples of frozen peas and spinach purchased from retail outlets had substantially higher antioxidant activity than canned or jarred samples. In a comparison of cooking methods, microwave and boiling for short periods had a negligible effect on total antioxidant activity, but substantial losses occurred after prolonged boiling in water.     

Incidence of Listeria monocytogenes in Market Samples of Fresh and Frozen Vegetables

Samples of the outer portions of fresh beets, broccoli, cabbage, carrots, cauliflower, corn, head lettuce, leaf lettuce, mushrooms, and potatoes, as well as frozen green beans, green peas, pea pods, and spinach were examined for the presence of Listeria monocytogenes using a 7-day enrichment procedure at 30°C. Samples were streaked on modified McBrides agar, and isolates were tested for characterization reactions. Fresh carrots, lettuce, and mushrooms, and frozen spinach were also examined using a cold enrichment procedure at 4°C. Samples were taken weekly, streaked onto modified McBrides agar, and were characterized. It was determined that no L. monocytogenes was detectable in any of these samples.