Frothing as a food processing technique : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology in Food Processing at the Faculty of Food Science and Biotechnology, Massey University

Abstract

In this work, two major topics have been studied using frothing techniques.

(I) Studies on the possibility of using frothing techniques for recovery of proteins from solutions have been conducted.

Using sodium caseinate protein, frothing studies on various possible factors affecting the enrichment ratio e.g. pH, concentration, pre-heat treatment, have been carried out. It was found that, to recover protein as soluble protein, is rather more theoretical than practical.

However, further studies on frothing insolubilization techniques (i.e. to insolubilize protein by frothing) have shown that, it was possible to recover up to 65% of egg white albumin from solutions. The key factor governing the recovery efficiency was the stability of the protein prior to frothing operation i.e. the less stable the protein, the greater the recovery. For egg white, the most important single factor in promoting the recovery was the effect of pH near the isoelectric point. When the same techniques were applied to cheese whey, no froth precipitation was experienced even after various efforts

to destabilize the whey proteins just preceding the frothing process. A postulate has thus been put forward to explain the results.

(II) Experiments have been carried out to investigate the possibility of using frothing techniques for removing some undesirable substances in citrus juices e.g. excessive essential oil in citrus juice, naringin in grapefruit juice. Studies based on model systems have shown that, while a large proportion of essential oil would come out with the froth, appreciable amount of naringin could be removed only when a suitable surfactant was used. When the frothing techniques were applied to natural orange and grapefruit juices, it was found that, by removing a significant quantity of oil, some flavonoids and possibly some limonin, the flavour of the juices could be improved as confirmed by taste panel results.

(III) In addition, on the basis of the experimental evidence, a tentative theory and proposed mechanisms have been put forward for the removal of undesirable substances in fluid food product using surfactant. [From Summary]