Involvement of Proteins in Cloud Instability of Shamouti Orange [Citrus sinensis (L.) Osbeck] Juice

• Published in: Journal of agricultural and food chemistry 1999-07, Vol.47 (7), p.2623-2631
• Main Authors: Shomer, Ilan, Yefremov, Tatiana, Merin, Uzi
• Format: Article
• Language: English
• Subjects: Beverages; Biological and medical sciences; Citrus - chemistry; Citrus sinensis; coagulation; colloids; flocculation; Food Handling; Food industries; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; heat coagulation; heat treatment; neutral sugars; orange juice; pectins; Plant Proteins - chemistry; proteins; sugars; turbidity
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf9807723

The present study provides evidence for the involvement of protein in cloud instability of natural orange juice. No heat-coagulable proteins were found in the serum. Insoluble cloud matter (ICM) was heat-flocculated following enzymatic pectin degradation (EPD). The degree of flocculation depended on temperature (from ∼50 to 75 °C) and was highest at pH 3.5. The fresh juice contained about 6.5 and 1.8 mg mL-1 of ICM and alcohol-insoluble solids of the serum (AISS), respectively. The ICM and the AISS contained, respectively, proteins (182 ± 14 and 119 ± 3 μg mg-1), galacturonic acid (37 ± 6.6 and 175 ± 1 μg mg-1), and neutral sugars (350 ± 44 and 338 ± 22 μg mg-1). EPD 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. Under electrophoresis, proteins of the AISS included bands in the range of 20−52 kDa and 10−14 kDa and those of the ICM at 22 and 50 kDa. Keywords: Citrus; cloud; neutral sugars; orange juice; pectin; pectinesterase; proteins