Photo by Scott Bauer, USDA Agricultural Research Service, Bugwood.org
Citrus farming worldwidedelivers an annual 140 million tons of oranges, tangerines and other citrus fruits, but much of the postharvest crop is lost before it reaches the market.
“Up to 30% of citrus fruit is lost to decay and disease following harvesting,” says food scientist Yang Shan, a member of the Chinese Academy of Engineering and head of the Dongting Laboratory in Changsha, China.
Shan’s team of 60 researchers and 70 postgraduate students is working to develop environmentally friendly ways to protect citrus fruit from decay and disease during processing and storage, while maximizing full use of the fruit.
OZONE TO REDUCE MOLD
Blue and green mold, varieties of fungi, are in the researchers’ crosshairs. Penicillium italicum and Penicillium digitatum are responsible for 90% of postharvest citrus fruit disease in China, says Shan. Chemical fungicides are commonly used to kill them but pose risks to human health and the environment. An alternative is to fumigate harvested fruit with ozone (O3). But information about ozone’s impact on citrus flavonoids is limited.
To address the knowledge gap, Shan’s team fumigated satsuma mandarins stored in the lab with ozone. They found that the treated satsumas had a lower respiration rate, reduced rot rate and better appearance than untreated fruit.
QUICK FREEZING
Another contributor to postharvest citrus waste in China is the seasonal nature of fruit production. Most citrus is harvested in November and December, and canning plants are often overwhelmed by the quantity of fruit in a short period.
To allow the citrus to be processed over a longer period, Shan’s group has worked on quick-freezing technology to store fresh oranges prior to canning. They identified the optimum freezing rate and temperature for maximizing quality. Consumers could not tell the difference from canned fruit that had not been frozen.
MEMBRANE REMOVAL
Shan’s team has developed a more environmentally friendly way to remove the membranes between citrus segments, a key step in preparing citrus for canning. Traditionally, membranes are removed by machine. A more environmentally friendly solution is to use enzymes to break down the membranes, says Shan. His team’s method produced neat segments with a low rate of segment breakdown for satsuma mandarins.
MORE SOLUTIONS
Peel removal in citrus processing contributes to fruit waste. In China, citrus peel is barely used except in small amounts for traditional Chinese medicine products and essential oils. Shan proposed a less wasteful way to process citrus. His proposal was to pulp the whole fruit before separating it into its different parts, using the whole-fruit pulp for reconstituted juice.
Waste can also be reduced by ensuring that the harvested fruit is the best type for the job. Shan’s team identified five varieties of navel orange and a sweet orange as best for juice from whole fruit processing. This knowledge can be used to “adjust planting schedules and expand the cultivation of different varieties to meet the demands,” says Shan.
Source: Nature Portfolio
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