Research On Key Technologies Of Low Temperature Preservation Of Spinach

Spinach （Spinacia oleracea） is native to central and southwestern Asia. Amongfresh leafy greens, spinach is not only abundant in vitamins （VA, VC, VB）, carotenoids,protein and minerals （Ca, Fe, P）, but also an important source of VB6, folic acid and K.Consequently, it has a high nutritional value and becomes more and more popularamong consumers. Leaves are the main edible parts of spinach, whose metabolism is themost vigorous. Postharvest spinach is very susceptible to decay, to wilt, and to loss ofgreen color due to intensive transpiration and respiration. As a result, the shelf life isusually very limited and the quality cannot be guaranteed.The key technologies of low temperature preservation of spinach was studied inthis paper, such as vacuum pre-cooling technology, storage temperature, modifiedatmosphere packaging. The sensory quality, and the nutritional indexes such as weightloss rate, soluble solids content, chlorophyll content, vitamin C content, and the agingphysiological indicators （membrane permeability）, and the safety indicators （nitritecontent）, were investigated during storage in order to measure the effects of thosepreservation technologies above. In addition, the quality kinetics of spinach duringdifferent storage temperatures were also studied, and based on these, the shelf lifemathematical model of spinach was established. The results were gotten as follows:1. The quality changes of film packaged spinach stored at（00.5）℃,（51）℃,（101）℃,（201）℃were studied during storage. The results showed that spinachstored at（00.5）℃had good preservation quality, which spinach packaged with filmcould effectively inhibit the increase in weight loss rate, the decomposition ofchlorophyll, the decline of sensory quality, and the increase in nitrite content, therefore,it would prolong the shelf life of spinach to35d.2. Experiments were carried out to investigate the effect of vacuum pre-cooling on physiological activities during cold storage. The results revealed that the increase inweight loss, relative conductivity and MDA content were inhibited, and the sensoryquality was improved by vacuum pre-cooling as the pre-processing. Meanwhile, thedecompositions of chlorophyll and vitamin C were delayed. Taking all these intoaccount vacuum pre-cooling treatment can significantly extend the shelf life of spinach.3. The effects of different modified atmosphere packaging （MAP） on thephysiological, chemical and quality of spinach stored at4℃were investigated. Sensoryquality, weight loss rate, chlorophyll content, ascorbic acid content, electricalconductivity and the nitrite content, were evaluated at different intervals of storage.Results showed that samples by MAP with10%O₂and10%CO₂or5%CO₂were thebest mixture of tested gases which led to better maintenance of the spinach externalquality （appearance and color）, as well as internal quality （fresh weight, chlorophyll,and ascorbic acid）. Sensory scores were also maintained. These conditions also had apositive effect on inhibiting the increase in nitrite content and thus extended theshelf-life of the spinach of7¹0d to30d by keeping nutritive value, appearance andtexture in comparison with other MA conditions.4. Kinetic models were investigated at different temperatures during storage. Thesensory quality and chlorophyll content at different storage temperatures （273,283, and293K） were accessed to investigate the relation between sensory quality andchlorophyll content, and the time and temperature. The kinetic models of chlorophyllcontent with respect to storage time and temperature were developed based onArrhenius equation. Results revealed that the changes in the chlorophyll content showedhigher fitting accuracy （R²ï¼ž0.9） with the zero order and first order chemical kineticmodel. Activation energies （EA） and rate constants （k0） of chlorophyll content wereobtained. They were107388.0870J/mol,3.5242×10¹⁸respectively. Taking50%chlorophyll content loss as the threshold, a mathematic model for predicting the shelflife of spinach was established. Accordingly, based on the chlorophyll content value, theremaining shelf life of spinach in the range of293²73K could be predicted.Meanwhile, the shelf life was also predicted by Q₁₀ model, and3T theory was appliedto simulate postharvest circulation. The prediction equation of shelf life in0¹0℃、10²0℃and the quality loss and remained shelf life during different time and temperature were also attained.5. On the basis of the above efforts, the cold chain processes of postharvest spinachwere drawed, including harvest, selection and grading, recondition and packaging,pre-cooling, the origin refrigeration, transportation, sales under refrigeration, wholesaleand distribution （grading once again, recondition and packaging）, retail andconsumption, and a detailed description of the main technical points during cold chainof spinach were also proposed. Furthermore, the operating procedures of postharvestspinach were standardized which would provide some theoretical basis for the spinachcirculation.