Postharvest Stress Research Articles

Effect of postharvest mechanical stress on quality and storage life of Chinese cabbage cv. Yuki

The effects of 3 common handling procedures and mishaps (dropping, compression and trimming) applied to Chinese cabbage cv. Yuki [Brassica campestris L. ssp. pekinensis (Lour.) Olsson] were compared to unstressed control cabbages. Heads were mechanically stressed by dropping from 50 cm onto a hard floor, by prolonged compression under 3 kg of weight before storage, or by repeated trimming of the outer leaves during storage. Cabbages were stored at 2°C for 9 weeks. Market quality of cabbages was not affected by the mechanical stresses, but storage for 9 weeks reduced marketable quality. Heads that were repeatedly trimmed produced less ethylene at the end of the storage period compared to the start, and less ethylene than the other treatments (due to the removal of outer senescing and rotting leaves); however, marketable yield was not improved.

Responses of strawberry fruit to 1-Methylcyclopropene (1-MCP) and ethylene

1-Methylcyclopropene (1-MCP), a competitive inhibitorof ethylene action, binds to the ethylene receptor toregulate tissue responses to ethylene. In this work,we investigated the effects of 1-MCP and exogenousethylene on ripening, respiration rate, ionicconductivity and peroxidase activity in strawberryfruit. Strawberry fruit can ripen without exogenousethylene treatment, but exogenous ethylene inducessecondary ripening processes. Results indicated thatstimulation of respiration by ethylene wasdose-dependent. Fruit colour development and softeningwere slightly accelerated by ethylene, but changes insoluble solid content were not. 1-MCP may/may notaffect the respiratory rise induced by exogenousethylene dependent on fruit maturity. Cycloheximide(CHI) reduced the ethylene-induced respiratoryincrease. Combinations of 1-MCP and CHI reducedrespiration more than CHI alone. 1-MCP and CHI did notinfluence the primary respiratory change in nonethylene-treated fruit. This indicates that ethyleneinduced respiratory increase may involve an ethylenereceptor in early harvested fruit, but not in laterharvested fruit. Exogenous ethylene stimulatedrespiration by regulating new respiratory enzyme(s)synthesis in strawberry fruit. Ethylene induced anionic leakage increase, and this was positivelycorrelated to fruit water loss and peroxidaseactivity. These results suggest that non-climactericfruit, such as strawberry, may have different ethylenereceptor(s) and/or ethylene receptor(s) may havedifferent regulatory functions. It may be thesecondary effect of ethylene to stimulate respirationin strawberry. Non-climacteric fruit ripening may berelated to the development of active oxygen species(AOS) induced by postharvest stress.

380 Chlorophyll Fluorescence and Prediction of `Iceberg' Lettuce Shelf-life

Chlorophyll fluorescence responds to a range of environmental stresses that affect horticultural crops. This technique has been used successfully to evaluate the quality of commodities after exposure to a number of postharvest stresses such as chilling, heat, and atmospheric stress. As well, chlorophyll fluorescence measurements have been incorporated as the main characteristics in shelf-life prediction models. Our objective was to evaluate the use of chlorophyll fluorescence measurements at harvest to predict the shelf-life of `Iceberg' lettuce. It was hypothesized that storage potential is influenced by the degree of stress induced by field conditions and that different cultivars, although grown under the same conditions, experience varying degrees of stress that can be detected by fluorescence measurements at harvest, even in the absence of visual differences in quality. The utility of fluorescence measurements was limited by inconsistencies in the development of the heads, such as maturity and leaf formation, and by variation among different areas of the same leaf. Fluorescence data from a homogeneous group of heads revealed that the variation associated with different areas of the same leaf was larger than that associated with measurements from different heads. Also, fluorescence readings from one leaf differed from those taken from any non-adjacent leaves. These sources of variation, along with strong cultivar-dependant differences in the fluorescence signal, were quite large, and hence, any trends in fluorescence measurements related to storage potential were not observed. Therefore, chlorophyll fluorescence at harvest does not appear to be a good predictor of lettuce storability.

The Influence of Gibberellic Acid (GA) on Postharvest Pitting of Citrus

Postharvest pitting is a citrus peel disorder that is characterized by the physiological breakdown of oil glands and is caused by high temperature storage waxed fruit. Pitting can be controlled by low temperature storage (>10 °C) or application of waxes with high gas permeability. However, refrigeration is costly and often difficult to implement while waxes with higher gas permeabilities have gloss values that are considered to be insufficient for consumer acceptance. Consequently, packers would like to control or predict pitting incidence prior to postharvest stress. Pitting incidence within a grove can vary dramatically within a season despite comparable postharvest handling. Thus, peel susceptibility may be not only variable, but alterable. Peel physiology is readily altered by early-season application of GA, a method currently used to retard peel maturation. Since the influence of GA on postharvest pitting is not known, we examined the effect of early-season foliar-applications of GA on peel quality of `Fallglo' tangerines and white grapefruit. Fruit were harvested throughout the season, washed, coated with shellac-based wax, and stored at 21 °C and 93% RH. GA applied with a silicone surfactant retarded peel maturation as indicated by greener, firmer peels. Pitting incidence was typically less for GA-treated fruit during the initial days of storage. However, GA suppression of pitting did not always persist throughout storage. GA did not affect internal levels of O2, CO2, ethanol, or acetaldehyde or weight loss. While the effectiveness of GA was not consistent, the results suggest that GA application strategies could be developed to suppress pitting. Also, GA treatments may help define factors that determine fruit susceptibility to postharvest pitting.

Effect of irradiation on vitamin C content of strawberries and potatoes in combination with storage and with further cooking in potatoes

The vitamin C content of four varieties of strawberry was determined before and after treatment with ionising radiation at doses of 1, 2 or 3 kGy and after storage for 5 and 10 days at 6°C, and also in potatoes which, having been allowed a period of one month to recover from the effects of post-harvest stress, were irradiated at a sprout inhibition dose of 0·15 kGy, followed by storage and cooking. Total ascorbic acid (TAA), ascorbic acid (AA) and dehydroascorbic acid (DHAA) concentrations were measured using the technique of ion-exclusion high-performance liquid chromatography. Results from analysis of the strawberry samples showed the DHAA content increased immediately following irradiation and must, therefore, be taken into account when reporting vitamin C levels in irradiated produce. In addition it was observed that whilst irradiation did affect the vitamin C concentration in all varieties of strawberry, the change was small in comparison with the large variations observed between varieties. With regard to potatoes results showed that, whilst irradiation, storage and cooking all had the effect of reducing vitamin C concentration, irradiated samples stored for 5 months had similar or marginally higher levels than their non-irradiated counterparts. Cooking did not markedly reduce TAA content of irradiated potatoes compared to non-irradiated potatoes and it was also noted that microwave cooking was more destructive than boiling in lightly salted water. ©1997 SCI

Total and differential haemocyte counts in western rock lobsters (Panulirus cygnus George) under post-harvest stress

Total and differential haemocyte counts (THCs and DHCs) were obtained from 36 white and 36 red western rock lobsters (Panulirus cygnus) that had experienced stress during capture and transportation. The lobsters were divided into three different groups on the basis of their holding time in the factory tanks and their health status (fresh arrivals, healthy and moribund). THCs were obtained with a haemocytometer from fresh haemolymph stained with gentian violet. THCs ranged from 2.5 106 to 15.9 106 cells mL-1 in the three groups, being lowest in the moribund lobsters. DHCs were obtained from haemolymph smears stained with both Giemsa and May–GrÜnwald. Three major haemocyte groups could be identified in lobster haemolymph: hyalinocytes, semi-granulocytes and granulocytes. The proportion of hyalinocytes in the three lobster groups ranged from 29.1% to 37.0%, that of semi- granulocytes from 51.1% to 62.9%, and that of granulocytes from 5.1% to 13.1%. The proportion of granulocytes declined in lobsters after they were held for 16 h in the factory tanks and was lowest in moribund lobsters. The results show that THCs and DHCs may be useful in assessing stress or health status in the western rock lobster or other lobsters.

Membrane effects in postharvest physiology

Abstract Plant tissue deterioration is of prime importance to food and horticultural scientists. Experimental evidence continues to be gathered supporting membrane damage as the key event leading to a cascade of biochemical reactions culminating in tissue deterioration and economic loss. In this paper, the sequence of occurrences in plant membranes during natural senescence and resulting from postharvest stresses are reviewed and compared. The picture emerging from numerous studies devoted to this topic is of membrane lipids undergoing extensive chemical degradation. Biophysical changes in membrane lipids and enzymatic and non-enzymatic lipid peroxidation leads to altered membrane properties and result in defects such as ion leakage and cellular decompartmentation. Postharvest stresses including chilling injury and freezing injury often lead to similar patterns of deterioration. However, it is too early to conclude positively that a truly universal mechanism for both senescence and postharvest stress-induced membrane damage exists.

Reassessment of the Role of Calcium in Development of Bitter Pit in Apple

From an extensive evaluation of the literature on effects of orchard factors on bitter pit development, the following hypothesis has been derived. The primary factor causing bitter pit is high gibberellin (GA) levels late in the season, likely resulting from excessive root activity. The increased GA levels may cause increased permeability of cell membranes in the fruit close to vascular bundles, thereby resulting in increased sensitivity of the fruit cells to post-harvest water stress. Water stress, especially after harvest, may trigger the mechanism of bitter pit development if the primary factor, establishing susceptibility, prevails over factors that reduce susceptibility. Calcium (Ca2+) deficiency could be a secondary factor, increasing an existing risk of bitter pit development. Ca2+ may stabilise the cell membranes and reduce their permeability. However, high GA levels may hamper its movement to the fruit. Externally applied growth retardants, or ripening-related endogenous GA antagonists in the fruit flesh (e.g. ethylene and ABA), could aIso reduce susceptibility to bitter pit, independently of Ca2+, by antagonising the GA effect. The limitations of the present systems, which use Ca2+ content of the apple fruit to predict bitter pit, may reflect the secondary function of Ca2+ in bitter pit development.

High‐performance liquid chromatography analysis of peanut phospholipids. II. Effect of postharvest stress on phospholipid composition

AbstractPeanuts are harvested in late September, and sometimes the harvest season can extend through most of October. When weather patterns delay harvest, the result may cause an immature crop, curing problems, rain damage, and freeze damage. All of the above stress situations can affect oil quality and flavor of the peanuts by altering phospholipid composition. Such changes are related to refining problems as well as flavor problems. A new high‐performance liquid chromatography (HPLC) method was used for the analysis of phospholipids from postharvest stressed peanuts. The concentrations of phosphatidic acid (PA), phosphatidylethanolamine (PE), and phosphatidylcholine (PC) were higher in immature seed when compared to mature seed. A slight increase in concentration was observed for phosphatidylglycerol (PG), and a decrease in phosphatidylinositol occurred in immature peanuts. All phospholipids increased in concentration except PG when peanuts were cured at a high temperature (40°C). When peanut seeds were frozen at −16°C (before curing), a significant increase in concentration was observed for PA and PG, whereas the concentrations of PC and PE decreased to very low levels when compared to the control. Where concentration permitted, molecular species were separated on a reverse‐phase column by HPLC.

Factors Affecting Postharvest Stress of Summer-dug Photinia1

Abstract Photinia Χ fraseri Dress (Fraser Photinia) plants were dug and burlapped in the morning and afternoon during midsummer with or without previous irrigation or antitranspirant treatment (di-1-p methene = Vapor Gard). Plants were shipped for one day, held for 2 weeks under lath, and then planted. Moisture stress, indicated by shoot water potential, was monitored throughout the study and survival was rated in September. Use of the antitranspirant and morning digging reduced moisture stress of plants. Morning-dug plants had 80% or greater survival even without irrigation. Afternoon digging gave low survival with or without irrigation but afternoon digging plus Vapor Gard gave 100% survival.

Prevention of Postharvest Stress Cracks in Husked Coconuts during Transit1

Abstract In a stratified shipment of coconuts (Cocos nucifera L.), stress cracks occurred more frequently in the top of the load. Stress cracks and coconut weight loss were directly related. Of the total number of cracked coconuts, 81% occurred within the top section of the load, 10% in the middle, and 9% in the bottom section; while 43% of the total weight loss occurred within the top section, 27% in the middle, and 30% in the bottom section. The average percentages of cracked coconuts for each treatment over all 3 sections were 13.1% for the nonwaxed control, 5.2% for carnauba wax-treated, and 0.4% for paraffin wax-treated.