The effects of water activity, particle size distribution and free fat content on flowability of grated and dried Parmesan cheese : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University, Palmerston North, New Zealand

Abstract

A study was made of the effects of water activity, particle size distribution and free fat content on flowability of Grated and Dried Parmesan cheese made by Greenwood Valley Cheese Company (GVC) and by Kraft. The three parameters were modified to span a wide range around the original level of each. Water activity (Aw) was decreased / increased through water sorption. A range of particle sizes for each of the samples was obtained by separating the samples into two fractions and then combining them together to different levels. Samples were sieved through a stack of sieves with different mesh sizes and particle size was expressed in terms of median particle size. A range of free fat levels was obtained by spraying samples with anhydrous milk fat (AMF). The response of flowability to changes in these parameters was assessed. Flowability was measured by using a rotating drum. The results in the preliminary study showed that flowability increased with increasing moisture content from 18 to 22%, which is in contradiction to the normal expectation from the literature. Therefore, the hypothesis: flowability increases with increasing moisture content / Aw was proposed. To test the validity of the hypothesis, several trials were conducted. The results in the first trial showed that flowability increased with increasing Aw from 0.66 to 0.79 for both GVC and Kraft products. The results also revealed a possible critical Aw between 0.79 to 0.83 at which the products could have their optimum flowability. In the next trial, additional values in the Aw range between 0.79 to 0.83 were included. The results showed that flowability increased with increasing Aw from 0.67 to the critical Aw value and dropped down above this value. The critical Aw values for GVC products were determined at 0.80 ± 0.01. Kraft's product did not show this increasing trend or the critical Aw value. A series of commercial samples with different Aw levels from two of each of GVC products were chosen to test the hypothesis. Variation in water activity naturally occurred during processing due to the slight changes in drying conditions. The results obtained on these commercial samples showed flowability increased with increasing Aw from 0.69 to 0.77, Therefore, the hypothesis has been proven. The study on the effect of particle size shows flowability also increased with increasing median particle size for both GVC and Kraft products. Of the methods chosen to plot cumulative undersize versus sieve size, linear regression is suggested rather than simply joining the points. This is because all the points are taken into account when linear regression is used. The study conducted on the effect of free fat shows that flowability decreased with increasing free fat levels from 16.8 to 26.3%. The sieve analysis results on the samples with different free fat levels show that median particle size increased from 721 to 1476 μm with increasing free fat levels from 16.8 to 26.3%. This was presumably caused by particle aggregation. The results show that the positive effect of particle size on flowability could not counteract the negative effect of free fat. Further study is required to confirm the net effect of free fat and particle size