Changes in α-amylase activity in honey during the freeze-drying process

A. Keke* and I. Cinkmanis

Latvia University of Life Sciences and Technologies, Faculty of Food Technology, Department of Chemistry, Liela Street 2, LV-3001 Jelgava, Latvia
*Correspondence: anete.keke@llu.lv

Abstract:

Honey is a natural product, which is appreciated for its sweetness, high nutritional value and health benefits all over the world. Despite all benefits, the usage of honey in food industry is limited due to its high viscosity. The use of dried honey could be an alternative to liquid honey, and would allow to use it as an additive in a range of many different food products such as sauces, beverages, yogurts etc. There are many parameters, which are used to determinate the quality of honey. α-amylase (diastase) activity is one of the most important criteria to determine the quality and freshness of honey. The aim of the present study was to investigate and compare α-amylase activity in liquid honey samples and freeze-dried honey samples. Overall, 18 honey samples were dehydrated using a freeze-drying method. Freeze-drying of the samples was carried out at – 50.6 °C and the pressure was 0.036 mbar for 72 hours. α-amylase activity in the honey samples was tested using Amylazyme test tablets. The obtained results showed variability in α-amylase activity after the freeze-drying process. As hydroxymethylfurfural (HMF) is another important quality parameter of honey, the content of HMF was determined in the samples by high performance liquid chromatography. In some samples the concentration of HMF after freeze-drying increased and was higher than it is allowed according to the International Honey Commission (for example, 55.75 mg kg^-1).

Key words:

Comparison of phenolic compounds and antioxidant activity of fresh and freeze-dried potatoes

R. Zarins¹, Z. Kruma¹*, L. Tomsone¹, S. Kampuse¹, I. Skrabule² and I.H. Konosonoka²

¹Latvia University of Agriculture, Faculty of Food Technology, Department of Food Technology, Rigas iela 22, LV-3004 Jelgava, Latvia
²Institute of Agricultural Resources and Economics, Zinātne iela 2, Priekuli, Priekuli municipality, LV-4126 Latvia
*Correspondence: zanda.kruma@llu.lv

Abstract:

Potatoes (Solanum tuberosum L.) contain a wide range of compounds with health benefits, and different techniques have been developed for the determination of these compounds. Freeze-drying is a common method for the preservation and preparation of samples for the analyses of bioactive compounds, but it is well known that drying influences the composition of food products. The aim of the current study was to compare phenolic compounds and antioxidant activity of fresh and freeze-dried potatoes. In the experiment 11 cultivar potatoes grown in experimental fields of the Institute of Agricultural Resources and Economics in 2016 were analysed. Potatoes were freeze-dried. Homogenized fresh and freeze-dried samples were extracted with an ethanol/water (80/20 w/w) solution. Total phenolic content (TPC) was determined using the Folin-Ciocalteu method, and the antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH˙) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assays. The highest TPC and radical scavenging activity were determined in cultivars ‘Peru Purple’ and ‘Blue Congo’ potatoes. Freeze-drying influenced all the tested parameters but more significantly the TPC, and for certain cultivars a reduction of more than 30% was observed. A strong correlation between TPC, DPPH and ABTS in fresh and freeze-dried samples was observed, r = 0.81, r=0.93, r = 0.92, respectively. It could be concluded that the effect of freeze-drying on TPC and antioxidant activity is cultivar dependent.

Key words:

antioxidant activity, freeze-drying, phenolic compounds, potatoes