We showed that 53 C for 20 minwas the optimum exposure for
‘Carabao’ mangoes and the best combination in controlling culture
growth of pathogens. In vivo application at this exposure, however,
did not yield significant reduction in anthracnose (48.71%e52.63%)
and stem-end rot (48%e60.86%) after 14 days. The present study
demonstrated that even the optimum exposure for ‘Carabao’
mangoes was inadequate in giving a high degree of postharvest
disease control. A considerable level of latent infection may have
been present on fruit surfaces as unwrapped fruit were used in our
experiments. The poor efficiency of HWT could be attributed to its
fungistatic action leaving active propagules after treatment which
develop overtime and cause decay on fruit. Moreover, the inconsistent
performance seen, for example variation in disease severity
within a treatment, has to be addressed. Severity indexes of
anthracnose and stem-end rot showed standard deviations ranging
from ±1.05 to ±2.98, remarkably higher than those treated with
fungicide (±0.69 to ±0.99). The volatility of HWT in practical use
agreed with the in vitro result of the present study i.e., high variation
in radial growth and spore germination of C. gloeosporioides
and L. theobromae.
A correct setting of water temperature is important as fruit
absorb heat. For example, a 22 L water bath preheated at 80 C fell
to 51.6 C with 20 fruit immersed. The temperature increased to
53 C after 3e5 min. This scenario would significantly affect the
performance of HWT to destroy latent infections since the desired
exposure is not achieved. To address the problem, the personnel in
charge must be knowledgeable in setting temperature ranges to
attain the correct exposure. Upgrading water baths with a precise
heating and control system would also help address the problem.
Recycling of water should be considered as fresh water is becoming
limited and this treatment will have an economic impact in the
future.
HWT at 53 C for 20 min had no negative effect on the overall
quality of fruit as fruit firmness, TSS, TA, color, and weight loss were
statistically comparable with the untreated controls after 14 days.
In ordinary conditions, firmness of healthy ‘Carabao’ mangoes decreases
as the fruit ripen which could be attributed to the activity of
enzymes that degrade pectic substances (Pantastico et al., 1984).
Yet heat treatment inhibits solubilization of the carbonate soluble
pectin fraction which is one of the main factors contributing to
firmness retention (Lizada, 1991). Fruit firmness is one of the most
widely used indicators of fruit quality.
TheHWT technology is a more cost effective alternative to vapor
heat treatment and has added benefits such as ease of use, less time
consuming, reliable, and it gives fruit surface sanitation to exclude
plant debris and disease control (Jacobi et al., 2001). For the time
being, HWT will continue as a popular postharvest protocol for
‘Carabao’ mangoes in response to export requirements imposed
specifically by Japan. Conversely, HWT efficiency has to be
improved as an effective quarantine procedure in preventing
anthracnose and stem end-rot on harvested mangoes. Biological
control agents (BCA) and/or generally regarded as safe (GRAS)
compounds may be integrated with HWT. Such a temperature and
exposure time as in this study could, however, retard the development
of the pathogen in the fruit, and thus create a vacuum that
could be exploited by BCA and/or GRAS. Naturally occurring
antagonistic bacteria or fungi and application of GRAS compounds