STUDIES ON PREPARATION AND ELECTROPIIORETIC PROPERTIES OF PROTEIN PRODUCTS FROM RAPESEED MEAL
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Date
1998
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Mahatma Phule Krishi Vidyapeeth, Rahuri.
Abstract
The present investigation was undertaken to develop
suitable processes to prepare protein concentrate and protein
isolates from the traditional rapeseeds. Rapeseeds (Cv. Swati)
obtained from the local market were dehulled with traditional
stone mtHi to obtain dhal and husk fraction. The whole seed,
dhal or hull meals were analysed for oil, protein, fibre, ash,
phenolics and condensed tannins with standard procedures. The
defatted dhal meal was used to prepare protein concentrate and
various protein isolates and their electrophoretic properties
were studied.
Dehulling of rapeseed was found to increase the
contents of oil, proteins and phenolics and a significant
decrease in the fibre content in the dhal meal. Washing of the defatted dhal meal with 70 per cent acetone was found to
remove about 68 per cent of the total phenolics of the meal.
However, this acetone extracted meal still exhibited gray to
brown colour which may not be acceptable for edible purpose.
When the defatted meal was extracted with ammonia
methanol-water twice to remove glucosinolates and phenolics,
produced a full-fat meal (53% oil and 25% protein) with light
yellow colour. The yield of full-fat meal was 82 per cent.
When this was further subjected to solvent extraction with
hexane, it removed all the oil and pigments to produce a
protein concentrate creamy white in colour, bland in taste and
found to contain 60.6 per cent proteins. The yield of such
product was 38 per cent of the original dhal meal. This
process thus yielded two products namely glucosinolate-free
full— fat meal and the creamy colour protein concentrate that
can be used for edible purpose.
Among the different solvents employed to solubilise
the proteins, sodium chloride solution at 7.5 per cent, pH
7.0, SHMP at 0.5 per cent, pH 7.0 or sodium hydroxide solution
at pH 12.7 with meal to solvent ratio of 1 : 40 was found to
extract maximum proteins. Among these, SHMP may be more
preferred because of its low concentration and neutral pH to avoid the damage to the proteins and amino acids. Among the
different precipitati'oYi techniques, isoelectric precipitation
was found to recover only 28.7 per cent of the solubilised
proteins, while ammonium sulphate precipitation was found to
recover about 98 per cent of the solubilised proteins. The dry
matter and meal protein recoveries were about 40 and 80 per
cent, respectively with ammonium sulphate precipitation which
were significantly higher than the isoelectric precipitation.
SDS-PAGE pattern of proteins from different products
indicated that a low molecular weight fast moving proteins
constitute a significant proportion of meal proteins that are
not precipitated either at IP 4.5 or by 50 per cent ammonium
sulphate. Precipitation of proteins by using two levels of
ammonium sulphate i.e. 50 and 100 per cent in succession
produces two protein isolates with combined maximum protein
recovery as well as with distinctly different elecrophoretic
properties.
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