Influence of storage under unfavourable conditions on the caking properties and fungal contamination of potato starch and wheat flour

Abstract

In recent years, there has been growing interest in the elimination of undesirable phenomena in the processing of bulk materials. In this study, the relationship between the mechanical properties of caking, as analysed with FTIR structural measurements, and the phenomena connected with fungal growth were investigated in wheat flour and potato starch. The materials were stored in high humidity conditions at room temperature (20 ± 2 o C) in order to rapidly cause caking. The results showed changes in cake strength, for which the maximum force recorded by the sensor during storage was assumed. For the potato starch, the maximum strength occurred on the 8th day of storage and amounted to 29.4 N. From that day, the level of strength in this powder started to decrease, however, an increase in fungal contamination was also observed. Day 8 also marked the beginning of structural changes in the potato starch, which were observed in the FTIR spectra. The results obtained suggest that the strength of the agglomerates correlates with structural changes and fungal contamination. K e y w o r d s: caking, food powders, mechanical properties, fungal spoilage, powder quality

Influence of Long-Term Storage on the Caking Properties Determined in Punch Test and Fungal Contamination of Potato Starch and Wheat Flour

“…This study showed that in sucrose samples caking can be initiated already in conditions with water activity above 0.75, but only above 0.8 does it become significant. A similar conclusion was drawn in our previous studies [ 22 ]. In high humidity higher strength values were observed in both wheat flour and potato starch.…”

“…It may suggest that the development of microorganisms could also affect the density of the potato starch layer and, thus, increase the strength value. A similar effect was obtained in the work Wajs et al [ 22 ], where the amount of fungal contamination affected changes in the strength of the resulting agglomerates. The shortening of the first linear growth is, therefore, the result of the appearance of a dense layer, observed as the second peak.…”

“…The cake strength values, in this case, are almost twice as high. Comparing the maximum cake strength values of potato starch obtained in this study (about 16 N) in conditions of 75% RH and the strength value obtained in the study Wajs et al [ 22 ] in conditions of 100% RH (about 30N), we can conclude that the strength, in both cases, almost doubled. Potato starch and skimmed milk powder belong to the so-called "sticky" powders, so we can assume that the powders belonging to this group will clump similarly, with cake strength values almost doubling concerning storage at 75% and 100% RH.…”

“…Similarly, in the experiment with 100% air moisture content of wheat flour, there was a continuous increase of strength over the period of time and significantly lower values than in potato starch. This result may be associated with insufficient possibility to form bonds between the particles and weaker tendency to caking [ 22 ].…”

“…However, there is a lack of experiments that combined the study of mechanical properties with the microbiological aspect of food powders. In our previous work [ 22 ], we tried to find a relationship between cake strength of agglomerates, structural changes, and fungal contamination during short-term storage in high humidity. This study is a continuation of mention topic, which was never examined according our best knowledge.…”