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Recommendations for Maintaining Postharvest Quality 


Trevor Suslow and Marita Cantwell Department of Vegetable Crops, University of California, Davis, CA 95616


Maturity Indices
Sprouts, plant seedlings consumed shortly after germination, are produced from many vegetable and agronomic plant seeds. Harvest maturity is highly regulated by germination (sprouting) conditions. The desired sprout length is the primary maturity index and harvesting is done at a relatively fixed number of days following radicle (root) emergence. Depending on seed type, harvest generally occurs 3 to 8 days after germination (Ex. alfalfa and sunflower, respectively). Examples of typical desired sprout lengths are given below;

Type Harvest Maturity (mm)
Adzuki 14 to 26
Alfalfa 26 to 38
Bean 26 to 38
Buckwheat 10 to 15
Brassica spp (broccoli, etc) 16 to 26
Garbanzo 26 to 36
Mung Bean 26 to 76
Radish 16 to 26
Wheat 10 to 15

 


Quality Indices
Sprouts should be clean, brightly colored for the type and free of damage, debris and decay. Bean sprouts should be etiolated (lacking noticeable green chlorophyll) with white root tips ( none to very limited browning). Sprouts are typically harvested and washed free of seed coats and non-germinated seed. If germinated in a solid medium rather than in hydroponic culture, sprouts are thoroughly washed to remove adhering materials.


Optimum Temperature
32°F (0°C). Rapid cooling is essential to achieve the full storage potential of seed sprouts. Under these conditions most sprouts may be expected to maintain acceptable quality for 5 to 9 days. Shelf-life at 36°F (2.5°C) is less than 5 days, at 41°F (5°C), and at 50°F (10°C) is less than 2 days. The high respiration rates and perishable nature demand distribution and short-term storage at 32°F (0°C). Although industry experiences with Mung Bean suggest the potential for damage, no symptoms of chilling injury have been unequivocally linked to this temperature regime.


Optimum Relative Humidity
95 – 100%


Rates of Respiration 
Mung Bean Sprouts

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 20°C (68°F)
ml CO2/kg·hr 9 – 11 19 – 21 42 – 45 NR

To calculate heat production multiply ml CO2/kgohr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day. (NR – not recommended)


Rates of Ethylene Production

Mung Bean 0°C (32°F) 5°C (41°F) 10°C (50°F)
ml/kg·hr 0.15 0.24 0.9

 


Responses to Ethylene
Low to Medium sensitivity. Ethylene effects are not considered to be a significant factor in the optimal handling and distribution regimes for sprouts.


Responses to Controlled Atmospheres(CA)
Packing sprouts in plastic “clamshells” with limited venting or in perforated film pouches helps maintain quality. One report on mung bean sprouts (CA) demonstrated that 5% O2 + 15%CO2 extended keeping quality.


Physiological Disorders
Freeze injury Sprouts are susceptible to freeze injury but sensitivity varies widely. Shoots become water-soaked and turn black. Roots appear water-soaked and glassy. Roots become soft quickly on warming and darken rapidly.


Pathological Disorders
Bacterial Decay (Pantoea agglomerans = Erwinia herbicolaPseudomonas fluorescens Biovar II, Pseudomonas marginalisPseudomonas viridiflava) is a common problem in many sprout types and will develop very rapidly in production systems as well as in postharvest storage, at warmer than optimum temperatures. High quality seed, proper pre-germination, seed treatments and postharvest refrigeration are the primary controls but washing sprouts in chlorinated or ozonated water (or other effective and approved disinfectant) will help control this decay and spoilage.


Special Considerations

Microbial Food Safety and Sanitation
Considerations Several types of seed sprouts have been clinically linked to several notable outbreaks of bacterial pathogens, especially in recent years. Multistate incidents of highly virulent Salmonella and enterohemorrhagic E. coli O157:H7 have been traced to the consumption of alfalfa, Mung bean, and possibly radish sprouts. Seed contamination has been positively identified as, at least, one confirmed source of contamination in several cases.

In 1998, the California Department of Health Services led a petition for Environmental Protection Agency (EPA) Section 18 registration of a 2% Ca(OCl)2treatment for alfalfa seed as the best available method to ensure elimination of pathogens from seed. Full EPA Section 3 registration is expected in 2000. The International Sprout Growers association has endorsed this treatment as a voluntary industry-wide standard.

Organic sprout growers are at risk of losing their organic certification due to above limit residuals of hypochlorite. Alternative treatments are being actively investigated.

The document Microbiological Safety Evaluations and Recommendations on Sprouted Seeds is available from the Center for Food Safety and Applied Nutrition at http://vm.cfsan.fda.gov/~mow/sprouts2.html


Postharvest Technology Research and Information Center
Department of Pomology
University of California
One Shields Ave., Davis, CA 95616-8683

Send comments and questions to Postharvest Technology Research and Information Center
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Produce/ProduceFacts/Veg/seedsprouts.html updated July 12, 2000

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