EFFECT OF COLLECTION PERIOD ON STORAGE OF MUZAO JUJUBE

XU Mu-dan， LIU Qing， LIU Yan， ZENG Ling-jun

(School of Life Science and Engineering,Shaanxi University of Science & Technology, Xi′an 710021,China)

0 Introductions

Muzao jujube is the kind of date, which another name is luliang jujube of mother. They mainly locate in Luliang region of Shanxi Province and Yulin region of Shaanxi Province along the Yellow River, which is the local cultivars and its annual output is more than 130 million kilograms of fresh dates[1]. Muzao jujube has a large fruit and beautiful color, appropriate sweet and sour, dense flesh texture, and less moisture content. After picking they are vulnerable to dehydration, softening, alcohol-based and decay, meanwhile they are not lasting storage. The important technical measure of ensuring fruits and vegetables′ quality and extension postharvest life is timely harvested. Different collection periods of muzao jujubes′ physiological changes in low-temperature conditions were studied, to determine the best collection period and the method of keeping freshness. It can provide the necessary technique and theoretical basis for achieving the long-term storage and processing.

1 Materials and Methods

1.1 Materials

Muzao Jujube (Yulin Jiaxian), 3,5-dinitro salicylic acid (Chengdu Kelong Chemical Reagent Factory, chemical pure), NaOH(Tianda Chemical Reagent Factory of Tianjin Dongli region, AR), 2,6-dichloro-indophenol (U.S. Sigma Company, chemical pure), K2CrO4(Fuchen Chemical Reagent Factory of Tianjin, chemical pure).

1.2 Experimental methods

Muzao jujubes were picked respectively on the morning in September 23 and October 13, 2009 by hand in Shaanxi Yulin Jiaxian along the Yellow River Beach, which were half-red stage and red stage dates, jujube stems were preserved well. They were pre-cooled 24 h after picking, removing disease, injury and bad dates, and then packed in the thickness of 0.03 mm PE fresh packaging bags. Each bag loaded 500 g dates, and each treatment repeated five times. They were stored in -1～+1 ℃ refrigerator. The initial indicators were three days of jujube indicators after harvesting, measuring indicators once every 10 days, taking 5 to 10 dates every time, determining physiological parameters according to quartation after pulp mixing.

1.3 Detection of indicator methodologies

(1)Total sugar: 3,5-dinitrosalicylic acid assay[2].

(2)Vc: 2, 6-dichloro-indophenol method[2].

(3)Total acid: direct titration[2].

(4)Ethanol: potassium dichromate oxidation method[3].

(5)Sensory indicators: hardness determined with the GY-1 hardness measurements, each treatment determined five fruits, correspond to the jujube surface peeled and every one determined 2 times. The probe entered into the flesh in the norm of 0.5 cm, the measured hardness was relative value, and then averaged 10 times hardness as the treatment value. Weight loss: the weight loss rate was determined the pre-storage weight and the end of storage weight. The changes were scaled as soft fruit rates, sensory and flavor varieties for the quality of jujube during storage.

2 Result and Discussion

2.1 Effect of collection period on the total sugar content of muzao jujube

Jujubes′ total carbohydrate included galactose, rhamnose, glucose and sucrose and so on. The total sugar content is a dynamic changeable process during preservation, a part of sugar will be consumed by respiration, and the other will be supplied owing to starch hydrolysis of polysaccharides during storage. The changing of total sugar content about different collection period of muzao jujubes shows in Fig.1 in low temperature during storage.

Fig.1 Variation of total sugar content Fig.2 Variation of total acid content

Fig.1 shows that the total sugar content of all-red jujube is higher than half-red jujube. The total sugar content of all-red jujube was the highest on 20 day, it was up to 45.29%, which may be starch and cellulose hydrolyzed single sugar is greater than the amount of consumed sugar being of breath. After then the single sugar of jujube constantly being consumed, but it dose not add through the hydrolytic of the starch, cellulose and so on, and then the total sugar content continue to decline. Nevertheless, the total sugar content of half-red jujube achieved the tiptop on 30 day, which was up to 24.41%. The total sugar content of half-red jujube fell to 20.89% on 60 day during storage, and its direction was more stable.

2.2 Effect of collection period on the total acid content of muzao jujube

It contains organic acids for example malic acid, citric acid, t-cis-aconitic acid, succinic acid and fumaric acid and so on. These acids involved in the citric acid cycle during storage, thus constantly being consumed. The changing of total acid content about different collection period of muzao jujubes shows in Fig.2 in low temperature during storage.

Fig.2 shows that the total acid content of all-red jujube is higher than half-red jujube. The total acid content of all-red jujube rose to 0.780% on 10 day during storage, and followed by gradually declining. The acid content decreased to 0.357% on 60 day. However, the total acid of half-red jujube presented first and then decreased, which reached the highest as 0.590% during storage to 20 days, and it decreased to 0.442% to 60 days.

2.3 Effect of collection period on Vc content of muzao jujube

Vc content is abundant in muzao jujube, ranking first among all the cultivation of fruit, its laudatory is “The King of Vc”. Vc is vulnerable to oxidative degradation in the fruits and vegetables. The changing of Vc content about different collection period of muzao jujubes shows in Fig.3 in low temperature during storage.

Fig.3 Variation of Vc content Fig.4 Variation of ethanol content

Fig.3 shows that Vc content of all-red stage dates declined as the extension of storage period, whose initial Vc was lower than Vc content of half-red jujube, and it can low 82.16 mg/100 g. Comparing with the original value, it reduced by 79.21% on 60 days during storage. But Vc content of half-red jujube rose first and then dropped during storage, which achieved the maximum of 571.72 mg/100 g to 30 days. Relative to the initial Vc, it decreased by 13.62% on 60 day during storage.

2.4 Effect of collection period on ethanol content of muzao jujube

Many studies have shown that dates were most likely to occurring anaerobic respiration and then produced ethanol in virtue of compact flesh during storage, resulting in wines of date and thus speeding up intenerate and decay. The changing of ethanol content about different collection period of muzao jujubes shows in Fig.4 in low temperature during storage.

Fig.4 shows that the ethanol content of muzao jujube increased as the extension of storage period. The phenomenon that the ethanol content of red stage muzao jujube increased was very clear. The ethanol content was up to 0.740 mg/kg on 60 day. Whereas the ethanol content of half-red muzao jujube was 0.198 mg/kg on 60 day during storage.

2.5 The changing of sensory characteristics of muzao jujube during storage

The sensory variation of date manifested as a result of maturity and aging during storage. Hardness would constantly decline as a result that the original pectin and cellulose hydrolyzed. Dates are easy to lose water and accumulate ethanol, it shows that peel shrink on appearance and smell the flavor of ethanol. Due with the continuing aging, the jujube will mildew and rot, because the ability to resist microbial invasion dropped. Therefore, indexes such as hardness, fruit-soften rate and weight loss are representative of the extent of aging date, it can be judged effects of preservation from the sensory.

Tab.1 Variation of sensory characteristics about collection periodon 60 days in low temperature during storage

Tab.1 shows that all-red muzao jujube was poorer than the half-red jujube on sensory and flavor on 60 days during storage, which is not conducive to store and process due to serious rotten and soften, meanwhile it had a clear flavor of ethanol.

3 Conclusions

The results showed that half-red muzao jujubes were more storable than red stage jujubes, besides BAN Zhaojun[4]and others considered that the eight mature Lingwu had the best effect of comprehensive preservation. Every nutritional quality of half-red stage jujubes changed a little during storage, especially the content of Vc kept relatively higher level, and the rate of fruit-soften was less the half than that of red, meanwhile the sensory characteristics changed little. From the view of whole effect, the stage of half-red jujube would be suitable for season sales and processing. This will provide the best basis of collection period for preservation and processing of muzao jujubes.

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