Pg. 26-33 Relationship between harvest date and post-harvest fruit quality after extended cold storage in ‘Madras’ litchi

To assess the effect of advancing harvest date on post-storage fruit quality in ‘Madras’ litchi, five 2 kg boxes of recently sulphured ‘Madras’ litchis were sampled on 16, 17, 18, 19, 20, 23, 25 or 26 January, 2006, from Bassan Packers, in the vicinity of Tzaneen. Sulphuring was carried out on the day of harvesting and packhouse delivery. Within two hours of sulphuring, the fruits were placed in cold storage at 5°C for 21 days. Fruit sub-samples (10 per box), removed just prior to cold storage, were used to assess various harvest-stage fruit characteristics, namely, skin browning incidence, pulp discolouration incidence, fresh and dry weight, circumference, juice pH, and juice total soluble solids content (TSS). Quality evaluations were carried out immediately after cold storage and three and six days subsequently, when skin browning incidence, pulp discolouration incidence, blue mould colonization incidence, fresh weight, juice pH, and juice TSS content were determined. The effect of dipping the fruits in Fungazil (ambient dip, 6.2 g per 10 l, a.i. imidazole at 750 g per l) for 5 minutes immediately after cold storage on subsequent blue mould colonization was also appraised. The fruits harvested on or after January 23 received this dip.

Moisture loss during cold storage and subsequently was excessive. Six days after cold storage, weight losses of 22% to 30% were general. The fruits had become visibly shrunken. Propensity to lose moisture and harvest date showed no clear relationship. Quality outturn, considered in terms of the percentage fruit not showing pericarp browning directly after cold storage, could be predicted to a reasonable degree of accuracy by the incidence pericarp browning and pulp discolouration at harvest (R² = 74%). The extent of weight loss, however, was seen to render all of the fruits unacceptable on cold storage termination. Blue mould growth commenced shortly after cold storage and became pronounced during the days following cold storage. This prevented the objective assessment of the quality attributes except for fruit weight 3 or 6 days after cold storage. Fungizil treatment immediately after cold storage delayed the occurrence of blue mould. Fruit deterioration was still marked, however, due to skin browning and moisture loss. Fruit appeal at harvest, seen in terms of pericarp browning and pulp discolouration incidence and juice TSS and pH, correlated with taste appeal directly after cold storage. It was considered that further research be aimed at assessing treatments reducing moisture loss from sulphured ‘Madras’ litchis during extended cold storage. The present study
supports the conclusion of signs of pericarp browning or pulp discolouration at harvest indicating unsuitability for export.

Summary:

• The study assessed the effect of harvest date on post-storage quality of Madras litchi, sampled from January 16 to 26, 2006, stored at 5°C for 21 days after sulphuring on harvest day.
• Fruit characteristics evaluated before and after storage included pericarp browning, pulp discoloration, fresh and dry weight, circumference, juice pH, and total soluble solids (TSS).
• Weight loss due to moisture was excessive during and after cold storage, ranging from 13% to 21% during storage and 22% to 30% overall, with no clear relationship to harvest date.
• Pericarp browning and pulp discoloration at harvest were significant predictors of browning after cold storage, explaining 75% of the variation.
• Taste attributes (juice TSS and pH) at harvest positively correlated with those after storage, indicating harvest quality affects taste appeal post-storage.
• Blue mold (Penicillium) colonization started shortly after cold storage, mainly on regions with pericarp exudates; dipping fruits in Fungazil fungicide post-storage delayed mold but did not prevent deterioration from browning and moisture loss.
• The study concluded moisture loss is the primary cause of quality deterioration, unrelated to harvest date once fruits are palatable, and fruit moisture retention treatments are needed to improve export viability.
• The findings support that signs of browning at harvest indicate unsuitability for export, emphasizing harvest timing and post-harvest treatments to reduce moisture loss as critical factors.