Influence of Microwave Radiation on Ripening of Dhakki Dates

Abstract

Research was conducted to investigate the impact of microwave (Mw) radiation for stimulating the ripening of Dhakki date fruits. The fruits picked at four sub‐Khalal (Doka) maturity stages well before the onset of ripening, were radiated for 10 to 50 s at three microwave power levels of low (210 W), low medium (360 W) and medium (480 W) intensity. The radiated samples along with nonradiated control were placed for ripening/curing at 40C under fluorescent light, dark or sun. The effectiveness of a treatment was evaluated by estimating ripeness after 24, 48, 120 and 144 h incubation. Ripening/curing of the fruits increased gradually during the incubation displaying no difference in the rate whether incubated under dark or light. However, the Mw radiation boosted up the date forming process seven times, reducing the curing period sharply from 288 h for the control samples to 40 h for the samples that were Mw radiated for 50 s at 480 W. The stage of maturity of the fruits also offered a positive response to the ripening process thereby enhancing yield of the product substantially and maturity levels at the late Doka stage with hardness level of 180–200 mmHg.cm−2 believed the attractive maturity range for the ripening. Moreover, the radiation at 480 W facilitated early harvesting of fruits prior to attaining optimum maturity stage, thereby saving at least two weeks hanging of the fruits on the tree, and hence the damage by monsoon rain is expected to be reduced while the desirable qualities of the dates are held intact. However, exposing the fruits beyond 480 W manifested heat roasting and resulted in undesirable baked flavor.

Accelerated ripening of Dhakki dates by artificial means: ripening by acetic acid and sodium chloride

“…However, sodium chloride used alone proved more effectiveness and the quality changes in terms of color, taste and appearance were more pleasant. Previously it was demonstrated that the ripening of Doka at 250 hardness units is triggered by application of an optimum dose of microwave radiation (Baloch, 1999;Baloch et al, 2003;Saleem et al, 2002). Since at present, considerable ripening also occurs in Doka with 250 hardness consequent upon the ripening activators, it proves beyond doubt that leaving the fruit on the tree for want of Dong formation through natural process, is quite unjustified.…”

“…The fruits were harvested in the month of August at the fully mature Doka stage of 250-hardness (Baloch et al, 2003) well before the onset of Dong formation. Healthy and non-infected fruits were selected, and brought to the research laboratory of the Department of Food Science and Technology, Gomal University for experimentation.…”

“…The fruits ripened by the control treatment showed a uniform softness throughout, though it was to a lesser degree. Previously the microwave radiation had also caused a uniform ripening throughout the fruit body (Baloch et al, 2003). Kalra et al (1977) also reported that salt and acetic acid produced surface ripening of the dates.…”

“…Average fruit weight (g) and pulp were recorded by averaging weight of the ripened seed-free fruits. A hardness testing device developed in the laboratory (Baloch et al, 2003) determined the texture of the ripened fruit. The degree of ripeness (which is a measure of yield) and the total soluble solids were determined according to the methods reported earlier (Baloch et al, 2003;Saleem et al, 2002).…”

“…Consideration must be given to picking of Dhakki fruits at the firm and stringent Doka stage, inducing ripening artificially and completing the processing well before the monsoon season. In our previous study we have reported on ripening/curing of Dhakki dates using microwave radiation (Baloch, Saleem, Dar, Baloch, & Baloch, 2003;Saleem, Baloch, Ahmad, & Baloch, 2002). Information regarding ripening of dates using salt and acetic acid is inadequate, and the few available reports are variety specific (Asif & Al Taher, 1983;Kalra, Jawanda, & Munshi, 1977), whereas data pertaining to Dhakki dates is scare.…”