481 Effect of Citric Acid and Storage Conditions on the Respiration Rate of ‘Wonderful’ Pomegranate Arils K. Banda, O.J. Caleb and U.L. Opara Postharvest Technology Research Laboratory South African Research Chair in Postharvest Technology Department of Horticultural Science Stellenbosch University South Africa Keywords: Punica granatum, respiratory quotient, citric acid treatment, postharvest Abstract Optimum postharvest pre-treatments and storage conditions play a significant role in retarding physiological responses and disorders as well as extending the shelf life of minimally processed fruit and vegetables. This study investigated the effect of citric acid (10 g/L) pre-treatment and storage temperatures (5, 10, 15 and 20±2°C) on the respiration rate (RR) of minimally processed ‘Wonderful’ pomegranate arils during 5 d of storage. Arils were dipped in citric acid for 1 min and respiration study was conducted using the closed system method. Physicochemical (colour, total soluble solids (TSS), titratable acidity (TA) and pH) attributes of arils were evaluated initially and after 5 d of storage in jars. Storage temperature and the interaction of temperature, citric acid and storage time had a significant influence on RR. Across all treatments, CO 2 respiration rate (RCO 2 ) increased from 2.8-28.3 ml/kg h, while O 2 respiration rate (RO 2 ) increased from 2.6- 27.2 ml/kg h. Storage temperature and time influence the respiratory quotient (RQ) of pomegranate arils. The RQ values ranged from 0.9-1.24 for both treated and non- treated arils. Significant changes were observed in redness of citric treated arils at 5 and 10°C, while a significant decrease in TA and TSS after 5 d of storage was monitored. However, TSS:TA ratio increased slightly across all the treatments. Low temperature combined with citric acid treatment was effective in retarding RR and maintaining quality attributes of pomegranate arils for 5 d. INTRODUCTION Pomegranate fruit (Punica granatum L.) is a non-climacteric fruit, with a relatively low RR, which declines over time during postharvest storage to a steady rate (≈8 ml CO 2 /kg h) when stored between 0 and 10°C for approximately 3 months, while synthesis of ethylene occurs in trace amounts (<0.2 μl/kg h) (Kader et al., 1984). The RR of pomegranate whole fruit was found two- to three-fold higher in comparison to fresh minimally processed arils, with an average RR value of 5.7 ml CO 2 /kg h and 2.7 ml CO 2 / kg h for whole fruit and arils (‘Acco’ and ‘Herskawitz’), respectively, stored at 5°C (Caleb et al., 2012b). López-Rubira et al. (2005) reported an average RR of 1.2 ml CO 2 / kg h for minimally processed arils (‘Mollar Elche’) stored at 5°C. Fresh or fresh-cut pomegranate fruit physiological responses are influenced by extrinsic factors such as temperature (Caleb et al., 2012a). For instance, increasing storage temperature from 5 to 15°C increased RCO 2 of pomegranate arils (‘Acco’ and ‘Herskawitz’) from 5.7 to 18.5 ml CO 2 /kg h (Caleb et al., 2012b). However, there is limited information on the effects of postharvest pre-treatment combined with temperature on the RR of pomegranate arils. Low storage temperature combined with modified atmosphere packaging (MAP) helps to slow down RR, reduce weight loss, and retards the rate of microbial growth, thus extending the marketable life of whole and fresh-cut produce (Sivakumar et al., 2008; Torrieri et al., 2010; Mahajan et al., 2014). Organic acids have been applied to slow down both enzymatic and non-enzymatic browning, texture loss, and microbial growth on fresh produce (Artés et al., 2007). Treatment of fresh-cut melon dipped in 0.52 mM citric acid for 30 s prior to MAP maintained microbial safety and prevented translucency and Proc. V th International Conference Postharvest Unlimited Eds.: G.A. Manganaris et al. Acta Hort. 1079, ISHS 2015