Rauheitsmessungen an Lebensmittelflächen—Erprobung einer methode an kartoffelgewebe

Zusammenfassung

Die Körnigkeit einer Lebensmitteloberfläche wird am Beispiel der Kartoffel untersucht. Da eine Gewebeoberfläche geprüft werden soll, muss das Prüfgut zunächst geteilt werden. Als Teilverfahren erweist sich das Schneiden in einer fixierten Vorrichtung mit einem gespannten Stahldraht bzw. bei hoher Gewebefestigkeit mit einem Messer als am besten geeignet. Optimiert wurden dabei Schneidwinkel, Schneidgeschwindigkeit und Schneidbewegung. Nach dem Trocknen der Oberfläche mit Warmluft wird ein möglichst formtreuer Abguss der Gewebeoberfläche erstellt. Zur Bestimmung der Rauheit wird ein Einkufentastsystem (Perthometer S 5 P) eingesetzt. Die vorgestellte Methode kann als begleitende Untersuchung zur Charakterisierung der Körnigkeit von Kartoffeln dienen.

Summary

The granularity of food surfaces is an important component of texture, which influences the overall assessment of testers. The inherent disadvantage of human sensitivity can be countered in part by instrumental measuring methods. The property ‘granularity’ of food slices can be determined indirectly as the rugosity of the surface, and the aim of this study was to develop a practical system for determining rugosity (Fig. 1 and 2). The ‘tactle tracer’ system could be used on small foods (Fig. 6), but for the high surface pressure on the tactile tip which prevents direct measurement on the food, and necessitates a hard cast having to be struck from a mould of the surface under test.

Different potato cultivars were used to study and optimise the stages in this process; slicing, drying, casting and measuring the rugosity. Best reproducibility was achieved using the following (standard) procedures:Cutting (Fig. 3 and Fig. 4): A taut steel wire was used for cutting, but at higher tissue firmness a knife was better (Fig. 7), since thecutting angle could range from >0° up to 10° with acutting velocity of 0.04 m sec⁻¹. There was hardly any effect on the relationship of the tangential to the normal components of thecutting movement (Fig. 10).Drying was with warm air e.g. using a hair-dryer, the optimum drying period was 60 seconds in our experiments (Fig. 11).Casting with the material ‘Technovit 3040, black’ (supplier: Kulzer) gave the best precision.Measurements of rugosity were made with the ‘tactile tracing’ Perthometer S5P (supplier: Perthen/Mahr), in which the sample can be scanned in any direction. Readings are taken simply from the attached meter.

Identical experiments using a microscopic method showed that the factors influencing rugosity definitely corresponded to starch grain and cell diameters. The rugosity of slices is not enough to characterise the granularity of potatoes, and other techniques such as the above microscopic technique should be used along with it. The conclusions could be tested further on other processees or foods and could moreover help clarify as yet unresolved phenomena associated with subjective testing.