Effects of water stress on the post-harvest quality of two leafy vegetables,telfairia occidentalis and pterocarpus soyauxii during storage

The effect of water stress (excessive water loss) on the post-harvest quality of two leafy vegetables, Telfairia occidentalis and Pterocarpus soyauxii, at ambient (30–35°C) and low temperature (10°C) was investigated in south-eastern Nigeria. The effect of seal-packaging the vegetables in polyethylene and paper bags on quality decline of the leafy vegetables was also monitored. Unsealed leaves of T occidentalis and P soyauxii rapidly lost water during storage at either ambient or low temperature. There were decreases in the chlorophyll, protein and ascorbic acid contents in the stressed leaves. Packaging of the leaves in polyethylene bags alleviated these losses. Sealing of the leaves in polyethylene bags also alleviated water stress.     

Effects of storage condition and domestic cooking on the quality and nutrient content of African leafy vegetables (Cassia tora and Corchorus tridens)

BACKGROUND: The main objective of this research was to determine changes in nutrient content of two African leafy vegetables, Cassia tora and Corchorus tridens, on cooking and storage under different temperature conditions, i.e. room storage (20 °C), refrigerated storage (4 °C) and frozen storage (?18 °C). RESULTS: The leafy vegetables were analysed for moisture, colour (Hunter L, a, b), texture, total chlorophyll, ascorbic acid, dehydroascorbic acid and total phenolics. Results indicated that the degradation of ascorbic acid was highest as a result of frozen storage, followed by room temperature storage. The dehydroascorbic acid content was correspondingly high in frozen stored leafy vegetables, whereas it was undetectable in the room temperature and refrigerated stored materials. The total phenolic content of the leaves increased with storage time while the total chlorophyll content decreased under all storage conditions. Domestic cooking resulted in significant additional losses of ascorbic acid following storage under all temperature conditions, with only 1–10% retention in the leaves and 50–60% retention in the cooking water. The green colour of the leafy vegetables was retained best under refrigerated and frozen storage, while the peak force and toughness of the leaves increased upon storage under all conditions. The moisture content of the leafy vegetables did not show any significant difference on storage. CONCLUSION: This study is one of few to report nutrient content changes on the same raw material stored under various temperature conditions and cooked domestically. Refrigerated storage resulted in the highest retention of ascorbic acid and green colour in the leafy vegetables. Copyright © 2009 Society of Chemical Industry     

Pak Choi (Brassica rapa ssp Chinensis L) quality response to pre-harvest salinity and temperature

The effects of pre-harvest salinity levels (1.7, 9.5 and 12.3 mS cm⁻¹) and temperatures (18, 21 and 25 °C) on the ascorbic acid and total chlorophyll contents of Pak Choi (Brassica rapa ssp. Chinensis L) were investigated. The relationships of these chemical contents with storage period (0, 7 and 14 days) and water loss were also monitored. Increased production temperatures significantly (p < 0.001) reduced the ascorbic acid and total chlorophyll (p < 0.01). Ascorbic acid content in leaves grown at various salinities was significantly (p < 0.01) reduced beyond 9.5 mS cm⁻¹. Total chlorophyll was not affected by these different levels of salinity. Ascorbic acid contents of harvested shoots fell rapidly during the first seven days of storage, most markedly in shoots taken from plants grown at high salinity. The pattern of chlorophyll degradation depended on the plants' production environment where higher temperatures resulted subsequently in rapid degradation during storage. For shoots grown at high salinity, the chlorophyll content was sustained during early storage. Linear relationships were apparent between water loss and ascorbic acid and total chlorophyll contents of shoots from the range of treatments. © 1999 Society of Chemical Industry     

Chlorophyll changes in some green leafy vegetables during cooking

Five green leafy vegetables commonly consumed in Nigeria (Talinum triangulare, Corchorus olitorius, Celosia argentea, Amaranthus hybridus and Vernonia amygdalina) were examined for their chlorophyll contents. These varied between 0.038% for Talinum triangulare and 0.137% for Vernonia amygdalina, with chlorophyll-a constituting between 68 and 75% of the total chlorophyll. By bringing the temperature of the leaves to 100°C, at least 56% of the total chlorophyll was lost, the rate of loss decreasing with the initial total chlorophyll content. When the leaves were blanched by immersion in boiling water, they showed a greater rate of chlorophyll loss. This was reduced when the pH was adjusted to 6.     

EFFECT OF DEHYDRATION ON PHYSICOCHEMICAL PROPERTIES OF MUSTARD, MINT AND SPINACH

Mustard, mint and spinach were dehydrated in a sun and cabinet drier and were subsequently studied for rehydration characteristics. Dehydration ratio ranged from 12.37:1.0 to 23.37:1.0, while rehydration ratio varied from 1.0:2.84 to 1.0:3.76 for three green leafy vegetables. The bulk density of dried vegetables varied from 55.1 to 171.5 kg/m³, whereas the angle of repose was in the range of 33.2–52.4°. Color values L, a, b and ΔE were reduced with blanching and drying. Retention of chlorophyll, β‐carotene and ascorbic acid in dehydrated products varied from 41.87 to 61.35%, 22.26 to 55.16% and 13.36 to 37.53%, respectively. On rehydration, the ascorbic acid retention was further reduced to 4.17–11.55%.     

Sugar Beet Grown Using Nutrient Film Technique: Yield and Nutritional Quality

Sugar beet (Beta vulgaris L cv Great Western Sugar) was grown using the nutrient film technique with a half-strength modified Hoagland nutrient solution to determine its biomass yield and nutritional quality. After 6 months, storage root and foliage weights per plant were 493·1 g and 551·0 g, respectively. Sucrose content in the fresh storage root was 118·4 g kg⁻¹ but was less than 10 g kg⁻¹ in the fresh leaves and petioles. Some nutrients in the leaves and petioles were analysed to evaluate their potential as a leafy vegetable. Fresh leaf protein, total dietary fibre, mineral (Ca, Mg, Zn, Fe and K), vitamin (carotene, ascorbic acid and thiamine) and oxalic acid concentrations were similar to those of consumer-accepted green vegetables.     

Snap Bean Quality Changed Minimally When Stored in Low Density Polyolefin Film Package

Snap beans packed in low density polyolefin film and stored at 5°C and 10°C were removed at days 0, 4, 8, 12, and 16 for quality evaluation. Chlorophyll content of beans stored at 5°C was not influenced by storage period. Pods stored at 10°C showed significant increase in chlorophyll after 4 days storage followed by a decline as time of storage increased. Hue angle and tristimulus a* corresponded more closely to chlorophyll content and were better indicators of snap bean color than chroma and tristimulus L* and b*. Weight loss, seed percentage and ascorbic acid were higher in pods stored at 10°C than in those stored at 5°C. Storage temperature and period had no influence on texture or soluble solids content.     

Properties of phosphatase from six varieties of apricot relevant to potential use in apricot air‐drying

Abstract

Apricot phosphatase measured with p‐nitrophenol phosphate as substrate, was present as soluble and membrane‐bound isoforms at levels per gram of tissue generally lower than those found in other fruits, vegetables and cereals. Properties such as substrate affinity, stability at acid pH, heat stability at 50 to 60°C (normal apricot drying temperatures), optimal reaction temperature of 58°C, and reactivity with ascorbic acid polyphosphate favor the use of phosphatase to catalyze the slow release of ascorbic acid over the 36 to 40 h required for air drying. A feasibility trial demonstrated that low levels of ascorbic acid polyphosphate present in the infusion solution (0.5 to 2 g/L) were insufficient to prevent browning, but levels greater than 5 g/L resulted in commercially acceptable dried fruit.     

Effects of gallotannin treatment on attachment, growth, and survival of Escherichia coli O157:H7 and Listeria monocytogenes on spinach and lettuce

Food-borne illness outbreaks are increasingly associated with fresh produce. Their high prevalence may reflect the lack of methods to effectively remove pathogenic bacteria from the surface of fruits and vegetables. This study evaluated the effect of antimicrobial gallotannins on attachment, growth, and survival of food-borne pathogens on green leafy vegetables. Spinach leaves and interior leaves of lettuce harboring high and low cell counts of background microbiota, respectively, were washed with tap water with and without added gallotannins. To account for the variability among organisms, green leafy vegetables were inoculated with strain cocktails of Escherichia coli O157:H7 and Listeria monocytogenes. Cell counts of L. monocytogenes were significantly reduced by the gallotannin treatment. Lower cell counts after storage for 8?days at 4?°C demonstrated antimicrobial effects of gallotannins retained on the surface of green leafy vegetables. Gallotannin treatments with 1?g/L did not inhibit E. coli O157:H7 but hindered their attachment to filter paper by up to 94?%. The addition of gallotannin-containing extracts from mango (Mangifera indica L.) kernels to the washing water did neither alter color nor texture of bagged fresh-cut products. In conclusion, gallotannin treatment significantly reduced surface contamination of green leafy vegetables with L. monocytogenes and reduced the attachment of cells of E. coli O157:H7.     

KEEPING QUALITY OF FRESH-CUT BITTER GOURD (MOMORDICA CHARANTIA L.) AT LOW TEMPERATURE OF STORAGE

Bitter gourd (Momordica charantia L. cv. Wanningqinglv) fruit is chilling sensitive and usually cannot be stored at a low temperature for a long period. To learn how the quality of the fruit might be influenced by cutting and storage temperature, whole and cut bitter gourds were placed in polyethylene pouches and stored at 2 or 10C. The results showed that the cutting enhanced the microbial growth, loss of chlorophyll (Chl), starch and ascorbic acid (Vc), and increased reducing sugar content, ethylene production and respiration rate of bitter gourd. The decrease of Chl, starch, soluble protein and Vc in the cut bitter gourd was significantly reduced by storage at 2C relative to storage at 10C. No significant indication of chilling injury in the cut or intact bitter gourd was observed during the storage for 7 days at 2C. These results suggest that fresh‐cut bitter gourd can be stored at 2C to maintain its quality with high levels of Vc, Chl, soluble protein and microbiological safety.     

The impact of home freezing on the sensory characteristics of ready-to-use leafy vegetables

BACKGROUND: Owing to the increasing trend of consumption of ready‐to‐use leafy vegetables, the necessity of determining the best conditions for their frozen storage and the considerable impact of freezing on their sensory attributes, research was carried out to determine the best freezing temperature and storage time for a mixture of Allium ampeloprasum, Lepidium sativum and Stureia hortensis. RESULTS: The results for freezing temperature at three different storage times showed that colour and overall acceptability at ? 18 °C were always ranked first (P < 0.05), while taste at ? 18 °C was ranked first on days 120 and 150. The results for frozen storage time at three different temperatures indicated that colour, taste and acceptability were not significantly different. CONCLUSION: Overall, the results of this research indicated that the sensory attributes of leafy vegetables during 180 days of frozen storage were affected mainly by freezing temperature rather than frozen storage time. Copyright © 2010 Society of Chemical Industry     

Changes in antioxidants and taste-related compounds content during cold storage of fresh-cut red sweet peppers

Changes in antioxidants (ascorbic acid, phenolic compounds and carotenoids) and in taste-related compounds (sugars and organic acids) content were monitored in fresh-cut red sweet peppers (Capsicum annuum L., local ecotype “Peperone Cornetto di Pontecorvo”) during 9 days of cold storage. Pepper slices were placed in polystyrene trays, wrapped with a polyvinyl chloride film, and stored at 4 °C or at 8 °C; besides, to evaluate the effect of a prestorage hot water treatment, half of the slices were subjected to a dipping treatment in water at 53 °C for 4 min, before packaging and storage. During storage limited changes in O₂ and CO₂ concentrations were observed within all packages. Storage temperature strongly affected weight loss: at the end of the storage time it was <3 and >10% in fruits stored at 4 and 8 °C, respectively. Sugars (glucose and fructose) content showed a significant increase (+11%) only in fruits stored at 8 °C; this change was due to a concentration effect associated to water loss. A higher increase (+23 and +17% in fruits stored at 8 and 4 °C) was observed in organic acids (citric and malic) content. Minimal processing and storage produced only a quite limited degradation of ascorbic acid. Both hydroxycinnamic acid derivatives and flavonoids accumulated in fruits stored at 8 °C (and not heat treated), whereas at 4 °C phenolics accumulation appeared to be partially inhibited. All the main carotenoids (capsanthin, cucurbitaxanthin A, zeaxanthin, β-carotene and β-cryptoxanthin) markedly accumulated in fruits stored at 8 °C (not heat treated), and showed a general decrease at 4 °C. Hot water treatment did seem to affect organic acids metabolism, though it did not promote ascorbic acid degradation. In addition, it inhibited both phenolics and carotenoid accumulation in fruits stored at 8 °C.     

EFFECT OF SOLUBLE SOLIDS AND TEMPERATURE ON ASCORBIC ACID DEGRADATION IN LEMON JUICE STORED IN GLASS BOTTLES

Lemon juice at concentrations of 9°, 20°, 30°, 40° and 50°Brix was stored at 10°, 20° and 36°C for 16 weeks and sampled regularly for total soluble solids (TSS), pH, titratable acidity and ascorbic acid. No significant differences were found in the first two of these factors as a function of storage time. There was a small but significant decrease in citric acid concentration over 16 weeks. Ascorbic acid loss was greater at higher temperatures; at a constant temperature, the loss was smaller as TSS increased. Ascorbic acid degradation data fitted zero-, first- and second-order models equally well at all five TSS. Rate constants in 9°Brix juice were significantly higher than those for the other four concentrations at all three temperatures. E_a values of 47.8 and 24.1 kJ mol^?1 were calculated for ascorbic acid degradation in 9° and 20°Brix juices. The effect of temperature far outweighed the effect of TSS on ascorbic acid degradation. Over the 16-week storage period, maximum retention of ascorbic acid (95.7%) was obtained in the 50°Brix lemon juice concentrate stored at 10°C.     

Influence of Water Stress on Cold-Induced Sweetening in Leafy Vegetable, Brassica juncea L.

The occurrence of low temperature sweetening in Brussica juncen L., an apparently chilling-tolerant leafy vegetables, has been investigated in relation to the effect of water stress and postharvest age (i.e. fresh harvest vs previously stored samples). The magnitude of cold-induced sweetening in B. juncea leaves was estimated to vary from 10–145% relative to the corresponding nonchilled samples. Previously stored leaves showed greater tendency to accumulate sugars but was apparently less responsive to cold-induced sweetening than freshly harvested leaves. Water stress synergistically enhanced this low temperature sweetening response; markedly greater and/or faster accumulation of sugars occurred in leaves that were both chilled and stressed. The majority of the total sugar increase was attributable to non-reducing sugars.     

A comparative study on the effect of packaging material and storage environment on shelf life of fresh bell-pepper

The effect of packaging materials [low density polyethylene (LDPE), polypropylene (PP)] and storage environment [modified atmospheric packaging (MAP)] on shelf life enhancement of bell pepper in terms of quality attributes such as physiological weight loss, ascorbic acid, texture, surface colour and subjective quality analysis have been studied at ambient and refrigerated condition. Different packaging techniques used for the experiment were MAP with LDPE, MAP with PP, MAP in perforated LDPE films, MAP in perforated PP films, shrink packaging with bi-axially oriented PP (BOPP) film and vacuum packaging with PP film. The in-pack bell pepper created a suitable headspace environment with low O₂ and high CO₂ concentrations, which resulted in a better retention of freshness of the vegetables and its marketability. Shrink packaging with BOPP film could not yield better result under ambient storage because of high water vapor transmission rate of the film and consequently loss of turgidity of the vegetables. Among different packaging techniques and storage conditions, MAP with PP film in refrigerated condition was found to be the best followed by vacuum pack with PP film in refrigerated condition and could be used to store for 20 days for bell pepper with maintenance of texture, colour, ascorbic acid and marketability. It is also inferred that under ambient conditions, bell pepper could be stored for 4 days using ventilated LDPE and PP as MAP storage. Further studies are needed to evaluate the sensory aspects, as well as to microbiological evaluation to characterize the fresh bell pepper during storage.     

A study of the apparent diffusion coefficients for ascorbic acid losses from peas during blanching in water

Blanching is an important pretreatment in the processing of many vegetables. The previous studies concluded that the major losses of ascorbic acid from peas during blanching in water are due to leaching process. Therefore this study is concerned with the loss of ascorbic acid from peas during water blanching at 50,60,70,80 and 90°C for 0, 2, 4, 6, 8, and 10 min, in an attempt to elucidate the mechanisms involved in such losses. When the agitation of the blanch water is sufficient, the surface resistance is made negligibly small, and the total resistance to the loss of ascorbic acid from peas to the blanch water is controlled by diffusion mechanism only. So the apparent diffusion coefficients (D) for ascorbic acid loss from peas were calculated after blanching under various conditions. When the temperature ranged from 50°C to 90°C, values of D were found to be in the range of 0.94 × 10^?8 to 1.94 × 10^?8 m² s^?1, having an activation energy of 18.71 kJ/mol. Also the results indicated that, if there was a sufficient agitation, the leaching of ascorbic acid from peas during blanching in water was controlled by “diffusion”.     

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.     

Degradation kinetics of ascorbic acid in encapsulated spray-dried honey powder packaged in aluminium laminated polyethylene and high-density polyethylene

The present study evaluated the stability of nutritionally rich encapsulated spray-dried honey powders in terms of hygroscopicity, glass transition temperature, total phenolic content, antioxidant activity and ascorbic acid using maltodextrin, gum arabic, and whey protein concentrate as carriers during a storage period of 180 days using high-density polyethylene and aluminium laminated polyethylene as packaging materials at 25°C (room temperature) and 35°C (accelerated temperature). The results revealed that temperature caused a negative influence on the glass transition temperature and stability of ascorbic acid. The kinetics of ascorbic acid degradation followed a first-order reaction with a reaction rate constant dependent on temperature and packaging material. Honey powder developed with whey protein concentrate as carrier agent and stored in aluminium laminated polyethylene pouches at 35°C possessed the highest antioxidant activity and ascorbic acid due to the presence of phenolic compounds in honey, aonla (Emblica officinalis. Gaertn), and basil (Ocimum sanctum) extract. The honey powders stored in aluminium laminated polyethylene pouches showed comparatively better antioxidant properties (total phenolic content, ascorbic acid, and antioxidant activity) and minimum hygroscopicity than the powders stored in high-density polyethylene at both the storage temperatures.     

Hot water and curing treatments reduce chilling injury and maintain post-harvest quality of 'Valencia' oranges

‘Valencia’ oranges [Citrus sinensis (L.) Osbeck] were harvested at optimal maturity and either dipped in hot water at 53 °C for 3 or 6 min or at 48 °C for 12 min or cured at 53 °C for 1 or 6 h or at 48 °C for 12 h. The fruits were not degreened, waxed or treated with any post‐harvest fungicides. All fruit samples were stored at 4 °C for 6 months following the treatments. Both hot water dip and curing treatments reduced chilling injury and decay when compared with the untreated control. The most effective treatments were curing of fruit at 53 °C for 6 h and at 48 °C for 12 h. Weight loss and juice yield were higher in cured fruits than those from other treatments, but the heat treatments had no consistent effects on titratable acid, soluble solids, ascorbic acid and peel colour. It was concluded that a pre‐storage hot water dip and curing at high temperatures might be beneficial in preventing chilling injury and decay of ‘Valencia’ oranges for 6 months of storage at 4 °C.     

Effects of Pretreatment and Dehydration Temperature on Color, Nutrient Retention and Sensory Characteristics of Okra

Moisture content, water activity, color, and concentrations of ascorbic acid and thiamin of blanched (boiling water with or without 0.1% SO₂) and unblanched okra, dried for 10 hr at 63°C or 14 hr at 52°C, were determined before and after 6 wk storage at ambient temperature. Sensory characteristics were evaluated after storage and rehydration of okra slices. Blanching in boiling water with or without 0.1% SO₂ resulted in protection of the characteristic flavor of okra. Blanching in SO₂ solution before dehydration produced greater ascorbic acid retention (p < 0.05) but a substantial loss of thiamine (p ≤ 0.05).