R.K. Pal

Relationships between storage disorders and fruit calcium contents, lipoxygenase activity, and rates of ethylene evolution and respiration in ‘Royal Delicious’ apple (Malus × domestica Borkh.)

Summary Experiments were conducted to determine the relationships between the occurrence of storage disorders in ‘Royal Delicious’ apple (Malus ×domestica Borkh.) and fruit Ca2+ ion contents, rates of ethylene evolution and respiration, and lipoxygenase (LOX) activity. Apples were stored at 0º ± 1ºC and 90 – 95% relative humidity and sampled each month, up to 6 months, for storage disorders, fruit Ca2+ ion contents, rates of ethylene evolution and respiration, and LOX activity. Storage disorders such as bitter pit, cork spot, and brown core appeared after 3 months and increased in frequency at subsequent samplings. Regardless of the presence or absence of storage disorders, fruit showed a decline in Ca2+ ion concentration during storage. Ca2+ ion concentrations (means of 3, 4, 5, and 6 month samples) were significantly higher in disorder-free fruit [0.419 mg g–1 dry weight (DW)] than in fruit showing bitter pit (0.329 mg g–1 DW) or cork spot (0.340 mg g–1 DW), but were not significantly higher than in fruit with brown core (0.393 mg g–1 DW). Conversely, LOX activity was significantly lower in disorder-free fruit [0.168 µmoles linolenic acid oxidised min–1 g–1 fresh weight (FW)] compared to symptomatic fruit. LOX activity increased with the duration of storage in all fruit samples. The rates of ethylene evolution (58.5 µl C2H4 kg–1 FW fruit h–1) and respiration (16.0 ml CO2 kg–1 FW fruit h–1) were significantly lower in disorder-free fruit than in symptomatic fruit. The rates of ethylene evolution and respiration increased between 3 – 5 months in storage. After 5 months in storage, they remained stable or declined in all fruit. The correlations (R2) between Ca2+ ion content vs. the presence of physiological disorders such as bitter pit (–0.77), cork spot (–0.75), and brown core (–0.64), and between Ca2+ ion contents vs. LOX activity were strongly negative (–0.94). In contrast; the correlation between LOX activity vs. physiological disorders was strongly positive. Our study concluded that an inverse relationship existed between fruit Ca2+ ion content and the occurrence of bitter pit, cork spot, and/or brown core, and between fruit Ca2+ ion content and LOX activity. Moreover, the relationship between LOX activity and the presence of storage disorders was strongly positive.

Post-harvest nitric oxide treatment reduces chilling injury and enhances the shelf-life of mango (Mangifera indica L.) fruit during low-temperature storage

Summary Low-temperature storage is an effective and commercial means to extend the shelf-life of fresh fruit. However, tropical and sub-tropical fruit are prone to chilling injury (CI) while stored at low-temperatures. Among these, mango (Mangifera indica L.) is highly susceptible to CI when stored below 13ºC. The objective of this study was to determine the effect of a dipping treatment in 1.0 or 1.5 mM sodium nitroprusside (SNP) on the incidence of CI and selected quality traits in mango (M. indica L. ‘Chausa’). Freshly-harvested, physiologically mature mango fruit were treated with the nitric oxide (NO)-donor, sodium nitroprusside (at 1.0 mM or 1.5 mM), by the immersion method, followed by storage at 8º ± 0.5ºC and 90 ± 5% relative humidity for 30 d. Before recording the effects, fruit were exposed to 25º ± 2ºC for 3 d to simulate shelf-life. The results indicated that dipping in SNP, irrespective of concentration, reduced the incidence of CI by 1.5- to 1.7-fold, electrolyte leakage by 26 – 41%, the rate of respiration by 47 – 59%, and the rate of ethylene production by 117 – 270% compared to control fruit dipped in distilled water. Furthermore, 1.5 mM SNP maintained a lower fresh weight loss (46%), a lower incidence of decay (220%), reduced pectin methyl esterase (81%) and polygalacturonase (30%) activities, and higher fruit firmness by 43% compared to control fruit. Electrolyte leakage was highly correlated with CI (r = 0.982), while fruit firmness showed a negative correlation with CI. These findings confirmed that 1.0 mM or 1.5 mM SNP can be used as a dipping treatment before low temperature storage of mango fruit to prolong its shelf-life and maintain its quality.

Response of kiwifruit (Actinidia deliciosa cv. Allison) to post-harvest treatment with 1-methylcyclopropene

Summary Experiments were conducted to observe the effect of different concentrations of 1-methylcyclopropene (1-MCP) on the post-harvest life and quality of ‘Allison’ kiwifruit (Actinidia deliciosa). Fruit were treated with 1-MCP at 0.5 µl l–1, 1.0 µl l–1, or 2.0 µl l–1, un-treated fruit served as controls. Each 1-MCP treatment was applied for 24 h at 20°C. After treatment, fruit were transferred to ambient temperature storage (22º ± 4ºC; 65 – 70% relative humidity) for 18 d, during which time observations on various physical, physiological, and biochemical parameters were recorded at 3 d intervals. Our results indicated that 2.0 µl l–1 1-MCP was the most effective treatment to delay softening and ripening in ‘Allison’ kiwifruit, as such fruit showed the lowest mean weight loss (9.8 ± 0.2%), the highest mean fruit firmness value (32.7 ± 0.2 N), and began to ripen only after 12 d in storage, whereas untreated fruit started ripening on day-6 of storage. The activities of fruit softening enzymes such as polygalacturonase (PG; 58.5 ± 0.3 µg galacturonic acid g–1 FW h–1), and lipoxygenase (LOX; 3.96 ± 1.3 µmoles linoleic acid oxidised min–1 g–1 FW h–1) were lower, and total phenolics (TP) contents (24.3 ± 0.3 mg 100 g–1) and anti-oxidant (AOX) activities (12.5 ± 0.03 µmol Trolox g–1 FW h–1) were higher in 1-MCP-treated fruit than in untreated fruit (PG, 98.3 ± 0.5 µg galacturonic acid g–1 FW h–1; LOX, 4.39 ± 1.0 µmoles min–1 g–1 FW h–1; TP, 5.3 ± 0.6 mg 100 g–1; AOX, 4.7 ± 0.02 µmol Trolox g–1 FW h–1, respectively). In addition, 1-MCP-treated fruit exhibited lower rates of respiration (48.3 ± 0.4 ml CO2 kg–1 h–1) and ethylene production (30.2 ± 0.02 µl kg–1 FW h–1) than untreated fruit (58.9 ± 0.6 ml CO2 kg–1 h–1; 38.7 ± 0.04 µl kg–1 FW h–1, respectively). Similarly, 1-MCP-treated fruit had higher titratable acidity (TA; 1.33 ± 0.3%) and ascorbic acid (AA) contents (115.9 ± 2.6 mg 100 g–1 pulp) and lower soluble solids contents (SSC; 8.33º ± 0.2º Brix) than untreated kiwifruit (TA, 1.0 ± 0.2 %; AA, 105.3 ± 2.2 mg 100 g–1 pulp; SSC, 13.7º ± 0.3º Brix, respectively). Thus, 2.0 µl l–1 1-MCP can be used for the post-harvest treatment of ‘Allison’ kiwifruit to enhance its shelf-life and marketability by approx. 6 d.

Impact of pre-harvest fruit-bagging with different coloured bags on peel colour and the incidence of insect pests, disease and storage disorders in ‘Royal Delicious’ apple

Summary An experiment was conducted to observe the effect of pre-harvest fruit bagging on ‘Royal Delicious’ apple (Malus x domestica Borkh.). On-tree fruit bagging was done using single-layer, non-woven spun-bound fabric bags of four different colours (light-yellow, blue, green, or red) on 15 July for 30 d before the expected date of harvest (15 August). The bags were removed 3 d before harvest (12 August) in each of two seasons (2010-11; 2011-12). All coloured bags had a significant influence on skin colour development and fruit quality attributes in ‘Royal Delicious’ apple. However, the light-yellow bags were most effective for the development of an attractive red peel colour (Hunter a* value = 52 ± 4.0). They also gave higher mean values for total anthocyanin concentration (TAC; 297.4 ± 21.9 mg cyanidin-3-glucoside kg 1 FW), phenylalanine ammonia lyase (PAL) activity (0.54 ± 0.03 µmol cinnamic acid produced min 1 g 1 FW), fruit firmness (38.6 ± 1.2 N), calcium concentration (5.38 ± 0.5 mg Ca2 100 g 1 DW), total phenolics concentration (TPC; 9.77 ± 0.25 mg gallic acid equivalents, 100 g 1 FW), anti-oxidant (AOX) activity (12.6 ± 0.35 µmol Trolox g 1 FW), soluble solids concentration (SSC; 14.5 ± 0.46 ºBrix), and ascorbic acid concentration (AAC; 29.3 ± 1.52 mg 100 1 g pulp) compared to blue, red, or green bags, or un-bagged apple fruit. Furthermore, light-yellow bags also resulted in the lowest incidence of San Jose scale insects (0.4 ± 0.2%) and diseases such as scab (1.03 ± 0.86%), fly speck (0.3 ± 0.3%), and sooty blotch (0.17 ± 0.15%) at harvest, and in storage disorders such as bitter pit, cork pit, and brown core. We therefore conclude that fruit bagging using single-layer, light-yellow non-woven, spun-bound fabric bags 30 d before harvest is beneficial for ‘Royal Delicious’ apple fruit colour and quality.