An investigating study of apparent viscosity decrease in rose hip soup

Abstract: A rose hip soup manufacturing company has significant problems with a too low apparent viscosity of their product. Compiled historical data between the years 2007 and 2015 proves that the problem has been present for at least 8 years with many batches that does not live up to current quality standards. The compiled historical data followed a pattern with lower or higher apparent viscosity in periods, and not as single and irregular values. Packages of rose hip soup were analysed during two production occasions and no relations between apparent viscosity and brix, pH, total acid concentration or vitamin C concentration were found. A high content of solids in the soup appeared to contribute to a higher apparent viscosity. Since the rose hip raw material is not heat treated before the pasteurization step in the soupprocess, apparent viscosity decrease was tested for possible content of active enzymes in the rose hip flour. The apparent viscosity decreased the longer the unpasteurized soup was allowed to rest before pasteurization. If the rose hip flour was added to a cooked and cooled soup-base, the apparent viscosity decreased over time from the point where the rose hip was added. Measuring the apparent viscosity with heat treated rose hip flour gave less decrease of the apparent viscosity. When only the soup-base without added rose hip flour was analysed, the apparent viscosity was stable over time. An external α-amylase analysis of rose hip flour detected activity of α-amylase in one of two tested flours. Actions to avoid unwanted enzymatic degradation could be to use rose hip flour that are free from enzymes, add the rose hip flour at a late stage in the production, or to heat treat the rose hip flour mixed with water before adding it to the mixing tank. To give a uniform content of solids, the stirring process could be increased in the sterile tank. The aims of this report were to identify the cause of the low apparent viscosity and to present solutions that could increase it. The aim was not to test the effectiveness of the presented solutions in large-scale production.