Influence of Pretreatments and Modified Atmosphere Packaging on Toughness and Quality of Asparagus Spears During Storage

We investigated the effects of different storage methods and pretreatments on the toughness and quality of asparagus spears (Asparagus officinalis L.). Two storage methods were assessed: modified atmosphere (MA) storage using film with an oxygen transmission rate of 10,000 cc.m(-2).d(-1).atm(-1), and conventional storage (CS) using perforated film. Pretreatments were: irradiation with UV-C (UV-C), a hot water dip (HWD), pretreatment with CO2 (CT), CO2 injection (CI), or a control without treatment (control). In all treatments, asparagus spears were stored at a relative humidity of 85% and 4 degrees C. Respiration and ethylene production rates were lowest after HWD treatment. In the MA storage conditions, CO2 content within the film package was maintained at 8-11% regardless of pretreatment, thus satisfying optimal MA conditions for asparagus. Oxygen content decreased immediately after asparagus was put into storage, regardless of pretreatment methods, but later recovered to 15%. Ethylene content increased on the first day of storage, but gradually declined to 6.5-8.5 mu L.L-1 by the last storage day. Regardless of pretreatment method, fresh weight loss during CS was less than 6.0%. In MA storage, asparagus packages in the CI treatment had a fresh weight loss of 0.8%, which was the highest among treatments. Asparagus tip firmness was no different across all CS conditions, regardless of pretreatment, but was lowest in MA-stored asparagus after HWD treatment. HWD-treated asparagus had the least firm stems, whether in CS or MA storage. The lignin content of both tips and stems was lowest when asparagus was pretreated with HWD. In CS asparagus, phenylalanine ammonia-lyase (PAL) activity was lowest when pretreated with HWD, but there was no difference in PAL activity between pretreatments in the MA storage condition. PAL activity was the lowest after pretreatment with HWD, regardless of storage method. In asparagus tips, there was no difference in peroxidase (POD) activity across all storage and pretreatment methods. In CS stems, POD activity was lowest after HWD treatment, but there was no difference in stem POD activity in any of pretreatment conditions in MA storage. CS asparagus had a greater off-flavor than those in MA storage, but was lowest when pretreated with HWD, regardless of storage method. Soluble solids content of asparagus decreased across all pretreatment methods, but was the highest in CS after HWD treatment; no difference in soluble solids content was observed across all pretreatment methods in MA storage. Hue angle and total chlorophyll levels of tips and stems were higher in MA-stored asparagus, but regardless of storage method, were highest in the UV-C and HWD conditions, indicating inhibition of the yellowing effect. Of CS asparagus, those pretreated with HWD had the best appearance, while those treated with UV-C or HWD had the highest visual quality results among in MA-stored asparagus. In light of these results, we deduced that MA storage at low temperature was the most effective for maintaining asparagus quality and extending shelf life, but ethylene production inside the packages accelerated toughness. HWD was the best pretreatment for inhibiting ethylene production, toughness, and yellowing, so is an appropriate method for maintaining the quality of stored asparagus.