Whey is a by-product of cheese manufacturing and can be used to make a fermented whey beverage. However, the beverage rapidly separates by sedimentation. The addition of a stabiliser to the beverage can improve the texture of the beverage and prevent sedimentation due to the viscosity increase. Chemically modified starches are used as stabilisers in the food industry. Nevertheless, consumer concerns have demanded for less synthetic chemically modified ingredients in foods, and instead prefer clean-label ingredients. Starch modified with lipids and xanthan gum can be regarded as clean-label. The objective of this study is to determine the effect of modified starch treated with stearic acid and xanthan gum, on the quality of a fermented whey beverage.
Firstly, the properties of maize and high amylose maize starch (HAMS) modified with stearic acid and xanthan gum alone and in combination was determined. Normal maize starch was pasted with and without the modifying agents for two hours at 91 °C under atmospheric pressure. HAMS was pasted with and without modifying agents under pressure (500 kPa) for 10 minutes at 121 °C followed by 91 °C for 110 minutes. The gel strength and thermal properties of the pasted samples were analysed. The flow properties and characteristics of the beverages with the modified starches were evaluated at set intervals over a 15 day period. The IKA® LR 1000 reactor vessel used in upscale-processing could only operate under atmospheric pressure and could thus not fully gelatinise the HAMS. As a result, only maize starch (pasted alone and modified with stearic acid and xanthan gum, alone and in combination) could be used as a stabiliser in the fermented whey beverage.
Maize starch pasted with xanthan gum had an increased pasting viscosity relative to maize starch alone. The viscosity of HAMS pasted with xanthan gum was lower relative to the HAMS pasted alone. The high temperature and pressure processing conditions that affect the pasting of HAMS could potentially have degraded the xanthan gum. This could be a reason why an increase in viscosity was not observed as with the maize starch. The presence of amylose-lipid complexes (with and without xanthan gum) in both the maize starch and HAMS that was pasted with stearic acid, resulted in an increased pasting viscosity. Furthermore, the amylose-lipid complexes prevented a gel formation in both starches, possibly by interfering with the retrogradation of amylose chains.
The differential scanning calorimetry showed that maize starch pasted with stearic acid had more crystalline amylose-lipid complexes than the maize control. Decreased amounts of Type II amylose-lipid complexes were observed for the maize starch pasted with stearic acid and xanthan gum. It is presumed that the xanthan gum interferes with the formation of the amylose-lipid complexes in normal maize starch. HAMS pasted alone had Type II amylose-lipid complexes. The abundant amylose content and higher pasting temperatures could be a cause for the prevalent formation of the more crystalline Type II amylose-lipid complexes. The viscosity of HAMS was too low to significantly impact the beverage, therefore it was not used in the beverage formulation.
The beverages with the modified starch had increased levels of viscosity, decreased levels of sedimentation and increased degrees of shear thinning relative to the whey beverage with no starch. The beverages with the stearic acid modified starch (with and without xanthan gum) had a lower viscosity, increased level of sedimentation and a smaller degree of shear thinning relative to the beverages with modified starch (with and without xanthan gum). The lower viscosity could be due to the lack of the retrograded starch. It is believed that the decrease in shear thinning could be attributed to the compact size of the amylose-lipid complex relative to the long uncomplexed amylose molecules. However, the beverages with stearic acid modified starch (with and without xanthan gum) showed more consistent flow properties throughout the 15 day period in relation to the beverages with modified starch (with and without xanthan gum).
Maize starch modified with stearic acid has potential as a thickener and stabiliser in a fermented whey beverage as it shows limited changes during storage and shows higher viscosity. Further research into the rheological and sensory properties of the whey beverage with starch modified lipids is recommended for a marketable product.