MODIFICATION OF SORGHUM STARCH AND ITS APPLICATION IN DAIRY PRODUCTS
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Date
2020
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ICAR-NDRI, KARNAL
Abstract
Sorghum is a climate smart crop but underutilised for human consumption because of thick
pericarp, pigmentation and presence of anti-nutrients. Sorghum has not been much exploited for
the manufacturing of value-added products, despite the fact that it contains 70%
starch. Therefore, starch modification is required to improve the physico-chemical and functional
characteristics of native starches. Among the various methods of starch
modification, hydrothermal treatment has potential to generate environment-friendly modified
starch. Therefore, the present work was carried out to standardize the process for sorghum starch
modification through High Moisture Treatment (HMT) and Annealing (ANN). Among the three
additives, application of 0.30% NaOH yielded starch with maximum purity. Further,
characterization of isolated sorghum starch revealed that the swelling power (g/g) and solubility
(%) were 6±0.50g/g and 3.48±0.83 % respectively; while water and oil absorption capacity (g/g)
were found to be 1.07±0.03g/g and 1.58±0.09g/g, respectively. HMT modified starch
exhibited significantly (p<0.05) higher dextrose equivalent (2.59 ± 0.01%), oil absorption
capacity (2.6 ± 0.7g/g) and water absorption capacity (1.76± 0.38g/g); however, it resulted
in significant (p<0.05) reduction in the swelling power (3.39±0.07 g/g) and solubility (2.44 ±
0.24%) of starch. The annealing treatment caused significant increase (p<0.05) in the oil
absorption capacity (1.49±0.13g/g), water absorption capacity (1.55±0.28g/g) and dextrose
equivalent value (3.31±0.00%) while, significant (p<0.05) reduction in the swelling
power (3.62±0.19g/g) and solubility (2.12±0.16%) was observed. Dynamic rheology
indicated that storage modulus (G’) for native starch (2990 ± 37 Pa) significantly (p<0.05)
increased in HMT-20-4 (3185 ± 73.25 Pa) and HMT-30-4 modified starch (4275± 49.24 Pa). The
native starch had crossover point of (786±71.14 Pa) and the maximum crossover was observed
in the HMT-30-8 modified starch (1873± 31.19 Pa). These results suggested increased
firmness in native starch after HMT modification thus indicating higher shear stability.
In ANN starch, G' was significantly (p<0.05) higher in ANN-55-6 (4456.67±411.17 Pa) and ANN-
55-12 (4463.33±218.14 Pa) than native starch (2440.91± 289.25 Pa). FT-IR results revealed the
increased organisation of double helices in the crystalline region of the modified starch. In
modified starch, the increased oil absorption capacity positively correlates with emulsifying
capacity, however, higher inter-molecular interaction was evident from the decreased
solubility, swelling power and enhanced crystallite perfection. Based on the rheological properties
and the functional properties, the HMT-20-4 and ANN-55-6 were selected for incorporation in
yoghurt at the rate of 0.5,1 and 1.5 % as texture modifier. Textural, rheological and sensory
analysis of yoghurt samples showed that 1.5 % HMT-20-4 starch was found best for incorporation
into the product. Findings of the present investigation revealed that the hydrothermal modification
of starch by HMT and ANN led to modified sorghum starch with higher shear
and heat stability with improved water and oil absorption capacity. Further, these modified
starches could be applied as a texture improver in yoghurt and related fermented dairy products.