David Picha

Citrus is the leading fruit crop category in Louisiana in terms of production area. Satsuma mandarins (Citrus unshiu) constitute over three-fourths of all Louisiana citrus acreage and are commercially grown on approximately 500 acres in multiple south Louisiana parishes. Recent economic reports indicate satsuma production in the state generates a total farm gate value of $6.5 million (Louisiana Summary, 2019). In addition, numerous southern Louisianians and residents of the southeastern U.S. have one or more satsuma trees on their property.

Consumer demand in the U.S. for specialty citrus, particularly easy-peel seedless mandarins, has increased significantly in recent years. Extending the duration of fresh satsuma fruit availability by proper post-harvest care and packaging is important in order to maximize the marketing period and value of the fruit. LSU AgCenter post-harvest studies were initiated to determine the additional market life extension and fruit quality that can be obtained for satsumas by using proper post-harvest temperature management and individual shrink-wrap packaging.

Initial tests were conducted to determine the suitable film type and thickness for maximizing the post-harvest market life of individually shrink-wrapped Owari satsuma fruit. Three polyolefin-based shrink-wrap films (Cryovac D955, Clysar HPG and Clysar ABL) of different thicknesses (45 and 100 gauge) were evaluated at storage temperatures of 4 and 21 degrees Celsius (39 and 69 degrees Fahrenheit). Individual fruits were inserted into a film sleeve and heat sealed on both ends with a manual L-bar sealer. The wrapped fruit was then placed in a heat tunnel to shrink the film tightly around the peel surface (Figure 1). Following film wrapping, the fruits were held under refrigerated storage at 4 C and at room temperature, which was 21 C with about 50% relative humidity to simulate commercial storage and marketing conditions. Individual fruit weight loss measurements from 40 fruits were taken weekly until loss of fruit marketability due to excessive peel shriveling or post-harvest decay.

At the end of the marketable storage duration for each treatment, the squeezed juice from four replications of 10 half-fruits per replication were analyzed for the percentage of soluble solids, which is one measure of sugar content; individual sugars; pH, which is a measurement of how acidic or basic the liquid is; titratable acidity, which is a measurement of acids in the juice; and individual organic acids.

The post-harvest market life for individually shrink-wrapped Owari satsumas stored at 4 C was extended to 20 weeks, compared to only seven weeks for unwrapped fruit (Figure 3). This represented a market life extension of up to 13 additional weeks over unwrapped fruit. The average weight loss from shrink-wrapped Owari satsumas stored for 20 weeks at 4 C was only 2%. This was in contrast to a 20.8% weight loss for unwrapped satsumas after reaching their marketable limit of seven weeks at 4 C. The market life of wrapped Owari satsumas held at 21 C was 18 weeks, with a weight loss of approximately 7.5%. The market life of unwrapped fruit held at 21 C was only two weeks, with a weight loss of 22.7%. Shrink-wrapping extended the market life of Owari satsuma fruit held at 21 C for an additional 16 weeks.

Increasing the film thickness from 45 to 100 gauge slightly reduced the amount of fruit weight loss after extended storage times. The reduced amount of moisture loss and absence of peel shriveling in the shrink-wrapped fruit after extended holding periods resulted in a much better external appearance compared to unwrapped fruit. Fruit soluble solids content was similar or slightly higher with storage time (Table 1). Fruit pH increased with time, while titratable acidity decreased. The concomitant increase in the sugar to acid ratio after extended storage times resulted in very good edible quality fruit. No significant difference was found in fruit composition or edible quality between fruit from the different shrink-wrap treatments.

The use of individual fruit shrink-wrap packaging can significantly extend the marketing period of satsumas. External appearance and the edible quality of shrink-wrapped fruit remained acceptable after extended storage durations. Utilization of the proper post-harvest storage temperature of 4 C in combination with shrink-wrap packaging will allow Louisiana satsuma growers to significantly extend their marketing season into the early spring months and potentially obtain higher market prices. In addition, the improved post-harvest treatments will provide consumers with longer availability periods of nutritious high-quality Louisiana citrus fruit.

David Picha is a professor in the LSU School of Plant, Environmental and Soil Sciences.

(This article appears in the spring 2022 issue of Louisiana Agriculture magazine.)

LSU AgCenter horticulturist David Picha demonstrates equipment used to shrink-wrap citrus fruit. Photo by Olivia McClure

Figure 1. LSU AgCenter horticulturist David Picha has studied whether shrink-wrapped citrus fruit has a longer market life. Photo by Olivia McClure

LSU AgCenter horticulturist David Picha has studied whether shrink-wrapped citrus fruit has a longer market life. Photo by Olivia McClure