Involvement of Proteins in Cloud Instability of Valencia Orange [Citrus s inensis (L.) Osbeck] Juice

The present study examined the involvement of proteins in cloud flocculation of Valencia orange juice. Marked differences in cloud instability were found between juices of different harvest dates. Heating of enzymatic pectin degraded juice from April and June harvests resulted in development of clum...

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Bibliographic Details
Published in:Journal of agricultural and food chemistry 1999-07, Vol.47 (7), p.2632-2637
Main Authors: Shomer, Ilan, Yefremov, Tatiana, Merin, Uzi
Format: Article
Language:English
Subjects:
Beverages
Biological and medical sciences
Citrus - chemistry
Citrus sinensis
clarification
coagulation
degradation
flocculation
Food Handling
Food industries
Fruit and vegetable industries
Fundamental and applied biological sciences. Psychology
harvest date
heat treatment
orange juice
pectins
Plant Proteins - chemistry
proteins
sugars
temperature
turbidity
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Summary:The present study examined the involvement of proteins in cloud flocculation of Valencia orange juice. Marked differences in cloud instability were found between juices of different harvest dates. Heating of enzymatic pectin degraded juice from April and June harvests resulted in development of clumps and their precipitation. Although the juice from both harvesting dates remained hazy, the juice of April harvest was more turbid than that from June. Usually clarification increases as the temperature increases from ambient to 125 °C. Clarification occurred at pH 2.5−4.5 and was maximal at pH 3.5. The clarification of the April harvest juice was markedly lower than that of the June harvest. The fresh juice contained about 5.2 and 1.7 mg mL-1 insoluble cloud matter (ICM) and alcohol-insoluble serum solids (AISS), respectively. The ICM and the AISS, respectively, contained:  proteins (244.5 ± 8.7 and 132 ± 1.8 μg mg-1), galacturonic acid (40 ± 0 and 120 ± 0 μg mg-1) and neutral sugars (270 ± 39 and 329 ± 23 μg mg-1). Enzymatic pectin degradation resulted in removal of a marked portion of the pectin, and was accompanied by partial removal of neutral sugars (mainly glucose and galactose) and some proteins from the pectic polymer in both AISS and ICM. Proteins of the AISS included major bands at 10−14, 20, and 28 kDa and those of the ICM bands at 22, 24, 26, and 45 kDa. Keywords: Citrus; cloud; neutral sugars; orange juice; pectin; protein
ISSN:0021-8561
1520-5118
DOI:10.1021/jf980773v