Quarantine treatment of citrus for insect disinfestation is sometimes needed to be able to export fruit to various trading partners throughout the world. Although chemical fumigation has been often used for this purpose, legislative pressure and consumer desire for organic products are prompting a search for non-chemical alternatives. Treatment with high temperatures is an effective means of disinfestation that can be achieved in a timeframe similar to that of fumigation. Treatment with HTFA is generally thought to be the gentlest means of heat treatment with regard to its effect on fruit quality (McGuire, 1991). Favorable results were reported regarding the effect of HTFA on citrus quality (McGuire, 1991; Miller and McDonald, 1997; Sharp and McGuire, 1996), which gave optimism that this could be a relatively easy and effective alternative to chemical fumigation. Based on these and other results, a method for HTFA treatment (T103-b-1) was published in the USDA APHIS treatment manual (APHIS, 2012). Other research, designed to examine the effectiveness of HTFA treatment of oranges under commercial conditions, however, found there to be problems with HTFA-induced flavor changes (Mary Lu Arpaia, personal communication). In another study, Obenland et al. (1999) found that flavor loss began to occur in navel oranges during the last 2 h of the HTFA treatment while heating to a core temperature of 47.2 °C as specified by the treatment protocol (APHIS, 2012).
Oranges contain a complex mixture of volatile compounds that are known to be very important in determining their flavor (Nisperos-Carriedo and Shaw, 1990). The volatile composition of these fruit is known to be influenced by maturity and by postharvest conditions (Obenland et al., 2008, 2009). Waxing especially is known to have a large impact on volatiles and flavor (Baldwin et al., 1995). Previous research has demonstrated that the amount of these compounds present in mandarin oranges can be altered in response to heat treatment, which can lead to an adverse effect on overall flavor (Schirra and D'hallewin, 1997). Obenland et al. (1999) found that HTFA treatment changed the quantity of a number of key volatiles in navel oranges and that the changes corresponded to the flavor loss that was observed.
More recently, a newer protocol (T103-a-1) has been published in the USDA APHIS treatment manual for the disinfestation of Anastrepha spp. in citrus (APHIS, 2012) that uses a final core temperature of 44 °C rather than the higher temperature of 47.2 °C that was used in our previous work (Obenland et al., 1999). The objectives of this study were to: 1) evaluate the impact of this newer, potentially less injurious protocol on navel orange sensory quality; 2) examine more closely the impact of fruit waxing on sensory quality as influenced by HTFA treatment; and 3) examine the effect of HTFA treatment on flavor volatiles to better understand the impact of this treatment on flavor.
APHIS2012Plant protection and quarantine treatment manual. Section 5 Treatment schedule T103. U.S. Dept. Agr. 5-2-59.
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