Process of heat treatment and changes in garlic properties

P. Kic*

University Czech University of Life Sciences Prague, Faculty of Engineering, Department of Technological Equipment of Buildings, Kamýcká 129, CZ165 21 Prague, Czech Republic
*Correspondence: kic@tf.czu.czs

Abstract:

This paper aims to present the results of research focused on the heat treatment of garlic (Allium sativum) into black garlic. The research compared three varieties of classic kitchen garlic (Dukat, Topaz and Sabagold), grown in the Czech Republic. The course of heat treatment in a hot air dryer was investigated at 60 °C. Changes in the weight and moisture of the samples were monitored gravimetrically for 78 days. The dry matter content was measured gravimetrically after drying at 105 °C. There were certain differences between the varieties studied. The intensive decrease in water content, dry basis u (g g^-1) during the first 20 days was the fastest in the Topaz variety, when it dropped below 0.4 (g g^-1) after only 9 days. In the Dukat and Sabagold variety water content, wet basis w (%), from the original values w = 62 to 66% dropped below 30% within 20 days, and in the Topaz variety below 20%. Changes in the colour of garlic cloves were measured by A CM-600d spectrophotometer. During the black garlic processing, its gradual darkening occurred. Lightness L* decreased in the Dukat variety from 80.39 to 27.47, Topaz from 78.29 to 29.09 and Sabagold from 83.64 to 28.72. In all varieties, colour changes occurred. Greenness (-a*) changed from the 9th day to a redness (a*) whose saturation gradually decreased. The yellowness (b*) of all varieties also decreased significantly.

Key words:

The course of drying and colour changes of alfalfa under different drying conditions

P. Kic

Czech University of Life Sciences Prague, Faculty of Engineering, Department of Technological Equipment of Buildings, Kamýcká 129, CZ165 21 Prague, Czech Republic
*Correspondence: kic@tf.czu.cz

Abstract:

One of the conditions for successful livestock breeding and efficient livestock production is to ensure quality feed. High quality feed for livestock is alfalfa, which has a very high nutritional value and its cultivation is also important for crop production in terms of improving the soil structure and nitrogen enrichment. The aim of this paper is to inform about the experimental investigations of alfalfa drying and colour changes under different drying conditions. The results of natural convection at 27.5 °C and 40% relative air humidity are compared with forced convection at 1.2 m s^-1 air flow velocity at the same air temperature and with results of drying by natural convection at 50 °C. The dry matter content was measured gravimetrically after drying in a hot air dryer at 105 °C. Higher drying rates shorten the time required for drying and earlier preservation and storage in the hayloft or in the hay bales. This reduces the risk of wetting of feed such by rain and degradation by fungi, etc. A shorter drying time is also important in terms of energy savings. The precise knowledge of the drying process and drying curves allows also to determine the appropriate time for storage and conservation for production of another type of fodder e.g. haylage or silage. The measurement results show a positive effect of higher drying speeds as well as increased air temperature. Higher drying air temperature during convection led to the partial lightening and greater yellowing of the feed.

Key words:

forced drying, moisture., natural drying, spectrophotometer, temperature