HARVEST MATURITY AND POSTHARVEST FACTORS AFFECTING THE SHELF LIFE AND QUALITY OF GRAPEFRUIT

Abstract

Grapefruit is an important fruit crop in the world as well as in Pakistan. This study was carried out to investigate the effect of different harvesting dates, storage temperatures, and pre-storage treatments of hot water, wax coating, pre-harvest spray of SA and Me JA on the shelf life and quality of Ray Ruby and Shamber grapefruit. The fruits harvested in month of December showed higher biochemical constituents than the fruits harvested during September, October, November and January. The fruits stored at 8ºC and analysed after 90 days storage showed minimum chilling injuries (3.55 and 3.22%) than the fruits stored at 6ºC (11.44 and 10.22%) in Ray Ruby and Shamber respectively. The fruits stored at 8ºC showed higher levels of TSS (6.67 and 6.97 ºBrix), ascorbic acids (38.87 and 39.21 mg/100g), total sugars (6.93 and 7.54 %), reducing sugars (4.33 and 4.93 %), non-reducing sugars (1.85 and1.08%), total phenolic compounds (135.35 and 141.56 mg GAE/100g), total antioxidants (57.56 and 61.97%), total cartotenoids (15.20 and13.81 mg/100g), total flavonoids contents (43.24 and 47.28 mgCEQ/100g ) and total limonin contents (10.18 and 12.84 μg/mL) 90 days after storage in Ray Ruby and Shamber fruits, respectively. Sweetness, sourness and general acceptances measured by sensory evaluation showed that the fruits stored at 8ºC were preferred by the panellist than the fruits stored at 6ºC as well as to those kept intact on the trees. Hot water treatment for 3 min + TBZ for 5 min showed higher TSS (6.82 and 6.98 ºBrix), ascorbic acids (34.43 and 43.50 mg/100g), total sugars (5.06 and 6.44%), reducing sugars (4.62 and 4.44%), nonreducing sugars (2.02 and 1.99%), TSS/acidity ratios (5.57 and 4.77), maximum organoleptic scores and higher phytonutrients such as total phenolic compounds (145.80 and149.90 mgGAE/100g), total antioxidants (57.25 and 60.44 %), total carotenoids (14.49 and 16.36 mg/100g), total flavonoids contents (49.03 and 51.98 mgCEQ/100g) and total limonin contents (11.97 and 10.99 μg/mL) with lower chilling injuries (0.66 and 0.44%) and fruit rots (4.44 and 3.88%) than untreated fruits in Ray Ruby and Shamber, respectively. Chitosan application @ 140 mg per -1 fruit maintained highest fruit quality parameters such as TSS values (6.93 and 7.21ºBrix), ascorbic acids (36.30 and 38.38 mg/100g), total sugars (6.24 and 6.67 %), reducing sugars (4.47, 4.71%), non-reducing sugars (1.76, 1.96%), TSS/acidity ratios (5.25 and 6.00) after 90 days storage in fruits of both cultivars. Maximum organoleptic scores, total phenolic compound (172.32 and 176.43 mgGAE/100g), total antioxidants (72.09 and 75.96 %), total carotenoids (17.09 and 18.98 mg/100g), total flavonoids contents (52.27 and 59.50 mgCEQ/100g ) and total 2 limonin contents (15.08 and 12.87 μg/mL) with minimum chilling injuries (1.58 and 1.33%) and fruit rots (0.66 and 0.33%) were also measured in same fruits. Pre-harvest sprays of SA@ 12mM and MeJA @ 5 mM showed higher biochemical parameters such as TSS (5.92 and 5.83, 6.17 and 6.09ºBrix), ascorbic acids (35.86 and 35.86, 39.17 and 39.17 mg/100g), total sugars (5.88 and 5.77, 6.31 and 6.18 %), reducing sugars (3.74 and 3.64% ,4.05 and 3.96%) and non-reducing sugars (2.14 and 2.14, 2.26 and 2.12%), TSS/acidity ratio values (4.29 and 4.67, 5.82 and 5.38 ) in fruits of Ray Ruby and Shamber respectively after 90 days storage. Maximum organoleptic scores for overall acceptance (7.33, 7.22 and 7.66,7.44) and higher total phenolic compounds (166.29 and 165.76,170.48 and 167.28 mgGAE/100g), total antioxidants (72.63 and 71.37, 75.34 and 74.21%), Total carotenoids (16.40 and 16.32,18.09 and 18.03 mg/100g), total flavonoids contents (55.74 and 53.43,58.30 and 56.04 mgCEQ/100g) and total limonin contents (11.95 and 12.04, 10.66, 10.78 μg/mL) with minimum chilling injuries (1.57 and 1.42 %, 0.0 and 0.0%) and fruit rots (4.23 and 3.90%, 0 and 0 %) were also recorded in same fruits. On the basis of the result of this study, the Ist December was observed as an optimum time for harvesting of grapefruit varities Ray Ruby and Shamber. Pre-harvest sprays of SA @ 12mM and MeJA @ 5Mm, pre- storage hot water treatment (53°C) for 3 mins + TBZ for 5 mints and Chitosan @ 140 mg per-1 fruit and storage temperature of 8°C was found the best for maintaining phytonutrient quality of grapefruit cultivars Ray Ruby and Shamber for 90 days storage.