The solid state fermentation of apple pomace using yeasts to produce an improved stock feed supplement : a thesis presented in partial fulfilment of the requirements for the Master of Technology degree at Massey University
Apple pomace is a waste stream generated from the apple juice extraction process and constitutes about 25% of the original fruit (Walter and Sherman, 1976). It contains a large amount of water and sugars, has a low pH and a small amount of protein. The total production of apple pomace in New Zealand is 2.7 x 10⁴ tonnes/year. At present, it is mainly disposed of by transportation to landfill areas, with a minor portion being used locally as a pig feed supplement. However, this main disposal method is a major cost and is also of considerable environmental concern. As the quantity of pomace produced is forecasted to increase gradually over the next five years, alternative treatments and disposal options will become necessary. This project involved the solid state fermentation of apple pomace with the aim of producing an improved stock feed supplement. The fermentations were conducted using a variety of yeasts with the purpose of improving the nutritional value by increasing the crude protein content. The effects of unsterilised media, moisture content and nitrogen addition were also addressed. Sterilisation of the apple pomace medium prior to yeast inoculation was found to be necessary due to the superior growth characteristics of a yeast from the natural biota. This yeast was isolated and identified as Kloeckera apiculata. The growth of Kloeckera apiculata on sterilised apple pomace was superior to that exhibited by Candida utilis Y15, Saccharomyces cerevisiae Y10 and Yarrowia lipolytica IFO1659. Schizosaccharomyces pombe H115 grew poorly on the apple pomace medium. A reduction in the moisture content of the apple pomace medium from 80% to 65% was found to have little effect upon the growth characteristics of C. utilis, Kl. apiculata and Sacch. cerevisiae. Ammonium hydroxide was the most effective nitrogeous growth substrate at improving the growth of Kl. apiculata, when used as a medium supplement. The growth of C. utilis benefited most from the addition of ammonium sulphate. Kl. apiculata growth on apple pomace supplemented with 1% v/w 2 N ammonium hydroxide achieved a maximum crude protein content of 3.5%, measured on a dry weight basis, after 48 hours. Kl. apiculata growth on pomace supplemented with 1% v/w 7.8 N ammonium hydroxide achieved a maximum protein content of 7.2%, measured on a dry weight basis, after 72 hours. Comparison of the amino acid profile of the microbially modified apple pomace (7.2% protein) with amino acid profiles recommended for growing pigs and breeding pigs revealed a deficiency in nearly all amino acids. This research indicates that the increased protein content of the apple pomace, due to yeast propagation, is still insufficient to qualify it as a suitable stock feed supplement. However, research into the effects of other fermentation parameters may lead to further improvements in yeast growth. As the pig industry is potentially the greatest market in New Zealand for a microbial biomass product such as this, feeding trials with growing and breeding pigs are essential to determine its nutritional value. These trials would have a major bearing on determining the commercial prospects of this apple pomace feed product. However, before any further research is conducted, consideration must be given to a new process which has been proposed for the extraction of apple juice. This process would result in an altered apple pomace waste stream and, if it was adopted for future commercial use, may reduce the applicability in New Zealand of the research results described in this thesis.