The citrus processing industry typically makes use of the juice of fruits, but the fibruous pulp is not normally used. Since this is expensive to dispose of (around US$10 a tonne, according to the study) and burdensome of the environment, there is considerable interest in putting such waste matter to work for the food industry.
Meanwhile, natural foods are making for one of the biggest trends in the food sector, as consumers are increasingly mistrustful of synthetic additives.
As the authors of the study, accepted for publication in the journal Food Research International, point out, aromas produced by microorganisms are considered natural; and solid state fermentation (SSF) has been used for making aromas by cultivating yeasts and fungi in low cost substrates.
The investigations centered around using Ceratocystis fimbriata with citrus pulp, and using other residues as carbon and nitrogen sources. The carbon sources tested were sugarcane molasses and soy molasses, and the nitrogen sources soy bran and urea.
C. fimbriata was chosen as it has the potential for synthesizing esters, grows quickly, and depending on the conditions can produce a wide variety of different aromas – including peach, pineapple, banana, citrus and rose.
The researchers carried out the experiments using 250ml Erlenmeyer flasks. The pH value was 6.0, temperature 30 degrees centigrade, initial moisture 75 per cent, and the innoculum rate was 1.107 spores/g of citrus pulp. The time period was 120 hours.
The volatile compounds emitted were measured using Headspace Analysis in a gas chromatograph.
The team concluded that the process yielded “promising results”. The best production of volatile compounds was seen when the citrus pulp was supplemented with 50 per cent soy bran, 25 per cent sugarcane molasses, and a mineral saline solution was used.
Under these conditions, the researchers achieved a production of volatile compounds of 99.60μmol/L.g.
Food Research International (Elsevier) – published online ahead of print
DOI: 10.1016/j.foodres.2009.01.016“Improving fruity aroma production by fungi in ssf using citric pulp”
Authors: S.C. Rossi, L.P.S. Vandenberghe, B.M.P. Pereira, F.D. Gago, J.A. Rizzolo, A. Pandey, C.R. Soccol and A.B.P. Medeiros