Process innovation and quality aspects of French fries

The development and evaluation of a new production process for French fries is described. Superheated steam was used to replace pre-drying in hot air and par-frying in oil, and vacuum cooling was used for cooling and freezing. Finish-frying was still carried out in oil. In this way a substantial reduction of energy use and environmental costs was possible. However, problems with product quality were encountered. The main problem was skin formation, which resulted in a tough crust with a fatty appearance after finish-frying. The new process was modified, and this improved the product quality considerably. Unfortunately, the resulting energy reduction was too limited to justify the investment required for the new process.

Furthermore, a new look into the quality aspects of French fries is presented using state-of-the-art equipment. A combination of sensory analysis, TextureAnalyser,andConfocalScanning Laser Microscopy was used to study crispness of French fries independent of moisture content and doneness. In this way a higher frying temperature was shown to increase crispness. Prolonged pre-drying in hot air caused blister formation, which was similar to the skin observed with superheated steam. Odour active compounds of French fries were identified using GC-MS and GC-Olfactometry. Subsequently, the release of some of these compounds was followed in real time with MS-Nose using assessors and a mouth model system. It was shown that increasing the frying time, adding salt, and also skin formation affect flavour release. Most of the identified flavour compounds originated either from theMaillardreaction or from lipid degradation.Acrylamideis formed in theMaillardreaction as well.Multiresponsemodelling ofacrylamideformation in a glucose-asparaginereaction system showed thatacrylamideis an intermediate rather than an end product. Early lipid oxidation was studied at frying conditions by following the decrease of the antiradical power. Frying French fries was found to slow down the decrease of antiradical power, suggesting that compounds withantioxidativeproperties migrate from the product to the oil.

In conclusion, the work described in this thesis has contributed to insights into physicochemical processes that occur in French fries on micro-scale, and how process conditions influence the product quality.