Heat Damage

Hot water immersion or rinsing while brushing may result in commodity damage, which typically is manifested as browning on fruit surfaces, uneven ripening, breakdown of the fruit flesh, and even enhanced rot development if the technique is not properly applied [13]. Incidence of HWT-associated damage varied between regions, harvest dates, and orchards [76]. Immersion of guavas (Psidium guajava L.) for 35 minutes in water at 46.1 ± 0.2°C delayed ripening by 2 days, but increased susceptibility to decay [77]. Immersion of Marsh grapefruit at 48°C for 2 or 3 hours significantly increased decay (>30%). However, if fruit were treated at 45°C for 3 hours, no decay symptoms were detected after 90 days' storage at 4°C [56].

Heat treatment has been associated with increased susceptibility to decay in a number of crops, such as nectarine [78] and papaya [79]. The increase in the incidence of rot is likely to be due to pathogens invading areas on the fruit injured by the heat treatment. Hot water dips at 45° C for 2.5 minutes did not control mold development caused by P. digitatum in clementines [78]. The significant water loss and softness of fruit dipped at 55°C for 5 minutes was due to heat damage causing cracks and pitting on the surface of the treated fruit and the expansion and collapse of the hypoderm cells [36]. HWRB at 60° C for 25 seconds caused heat damage as irregular reddish pits of 0.5 to 1.5mm in diameter [16]. Heat damage on HWRB-treated apples (60°C for 15 seconds) appeared as round brown sunken pits [32].

Hot water dips can change some biochemical properties in minimally processed (peeled and trimmed) onions. Dipping prepeeled onions in 80°C for 1 minute resulted in irreversible membrane damage [80]. Dipping heads of fresh broccoli (Brassica oleracea L. Italica group cv. Paragon) at 52°C for 3 minutes enhanced off-odor development and caused visual damage to newer buds [81].

Hot water treatment of mandarins at 56 and 58°C for 3 minutes induced heat damage in the form of rind browning [62]. Hot water treatments for 10 minutes at 48°C and below were noninjurious to both yellow and green lemon fruit, with injury in the form of lesions on the rind beginning to occur at 50°C (yellow) and 52°C (green), and increasing in severity up to 58°C, the highest temperature tested. Emanation of d-limonene increased correspondingly with increasing injury. Green lemons were injured more severely than yellow and tended to release more d-limonene, especially at higher temperatures [82]. Heat damage was evident in avocado fruit as hardening of the skin when fruit ripened [83]. However, Obenland and Aung [84] reported that sodium chloride at a concentration of 200 mM reduced hot water damage in nectarine cultivars by effectively reducing the amount of water entering the fruit during hot water treatment.

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