Changes in the diastase activity of linden honey due to heat treatment, and during storage

Tuesday, September 30, 2014

1. Introduction

Of the enzymes found in honey, diastase is one of the most important ones, in fact, there is a separate limit value given for this parameter in the regulation of the Hungarian Food Codex regarding honey. Generally, the minimum diastase number is 8 (see definition later), or in the case of honey with low natural enzyme content, the expected value is at least 3. Diastase (a mixture of α- and β-amylase) is an enzyme that breaks down starch, which results mainly in maltose. The enzyme enters the honey during ripening from the hypopharyngeal secretions of bees, and its quantity is influenced by the composition and concentration of the nectar, the age of the bees and the intensity of the nectar flow [3]. Its presence in honey is one of the basic criteria of genuineness. Good quality honey usually has a high diastase activity.

 

The diastase content of honey can decrease significantly due to long-term storage or heat treatment, but is also

known that certain types of honey (e.g. acacia, orange, eucalyptus) contain low concentrations of diastase to begin with. This is explained by the fact that the nectar of certain plants has a higher dry matter content, therefore, less enzyme material is added to it during the shorter thickening period by the bees. Of the parameters routinely analyzed in honey, determination of diastase activity has the highest measurement uncertainty, therefore, relatively large deviations (20 to 30%) from the average are accepted by accreditation bodies during international proficiency tests. The diastase activity of honey can be determined based on the degree of degradation of starch [2],[4],[6],[7],[8],[9]. Generally, a starch solution of a given concentration and honey are incubated together, and at the end of the experiment either the amount of remaining (undegraded) starch solution or that of the fragments is determined, usually by a spectrophotometric method.

 

The characteristic value thus determined is the Goethe number (diastase number), which specifies the amount of 1% starch solution in ml that is degraded over one hour at 45-50 °C by the diastase enzyme contained in 1 g of honey. This value is usually somewhere between 10 and 18, but in the case of certain types of honey it can be lower (8-10) or higher, depending on the species. The lower limit is 8, below this the honey is considered spoiled or bad quality. Too low enzyme activity might indicate unripeness, inappropriate storage or improper heat treatment, therefore, diastase activity is one of the important parameters of honey qualification [1]. This factor is also greatly influenced by the acid content of honey: its optimum operating pH is between 5.0 and 5.2, at neutral pH the enzyme activity is low, and at strongly acidic pH (pH < 3.3) the enzyme decomposes rapidly. In the present paper, investigations of the effects of storage and heat treatment on diastase activity are reported, in the case of linden honey.

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