The effect of type (Astragalus, Ziziphus, Citrus and Thyme), and storage conditions on the most important qualitative characteristic of honey

Introduction: Honey is a bee product with appropriate organoleptic characteristics and high nutritional value. Vegetative source, climate conditions, time of nectar collecting, bee specious, and also storage condition of product are effective factors on its quality. During the process and storage stages, chemical reactions such as maillard change the quality and nutritional characteristics of the product. The effectiveness of these reactions depends on various parameters such as primary component’s nature, water activity and pH of product as well as the product storage conditions. Different factors such as, carbohydrate content, enzyme activity, hydroxymethylfurfural (HMF) are introduced as criteria in evaluating qualitative characteristics of honey. HMF is one of the most important factors in this group. It is a consequence of thermal process on foods containing high quantity of fructose and glucose. Therefore, it is considered as an important index on heating and shelf life of this product. In the first step of the present research, qualitative characteristics of four usual Iranian honeys were evaluated. Then, in order to study the effect of storage condition, the quality changes of products at different temperatures and times of storage were investigated. Materials and methods: In the first stage of the present research, qualitative characteristic (fructose/glucose ratio, sucrose, polyphenol content, hydroxymethylfurfuran, moisture, free acidity, lactic acid, total acidity, pH, color, diastase and electrical conductivity) of four Iranian honey (astragalus, ziziphus, citrus and thyme) collected in random sampling were measured. Then, effect of storage temperature (4, 23, 30 and 37°C) on changes of important qualitative characteristic of product (hydroxymethylfurfural content, polyphenol content, pH, color characteristic) were evaluated monthly for six months. Results and discussion: According to results, qualitative characteristics of samples were significantly different since the beginning of storage (p≤0.05). Moisture content of samples varied from 14.5 to 16.5%. PH was found to be 4.38 to 4.94, and total acid content ranged from 6.92 to 16.32%. The highest sucrose content was observed in ziziphus honey and the highest fructose-glucose ratio and pH were observed in astragalus honey. Thyme honey contains the highest diastase activity, acidic compounds, and the lowest amount of moisture and pH and ziziphus honey had the highest amount of acid lactic and electrical conductivity (142/0 mmol/cm). The amount of HMF in ziziphus honey was higher than other kind of samples (28.29 mg/ kg), and the content of these component were lower than 5 mg/kg in astragalus and citrus honey. All of the four samples were in permissible range according to maximum acceptable HMF content based on both Iranian national standard and honey international commission (40 mg/kg). In appearance characteristic, L* (brightness) of thyme and citrus honey were more than others and the highest greenness was observed in thyme honey and the highest yellowness were observed in astragalus and ziziphus samples. In the present study, the polyphenol content of samples was 23.33-39.33 (mg gallic acid in 100 g of sample) and thyme honey contained the highest polyphenol content. Diversity in floral is one of the main reason for differences in the qualitative characteristic of samples. Changes in mineral content, phenolic components, and floral origin were considered as the main effective factors in color changes of honey types.  Storage condition and honey type had significant effects on qualitative characteristics of product. Increasing time and storage temperature reduced brightness and hue angle, and increased chroma index in all kind of honey. By increasing the temperature and storage time, undesirable HMF content of samples were increased. Among the studied conditions, the best storage temperature in control of HMF content of product was 4 °C. Increasing storage temperature and time decreased the phenolic compounds of samples until the third month, and after that it was increased. In this regard, the effect of higher temperature on increasing polyphenol contents of product was more obvious. This observation is a consequence of secondary compounds formations from browning process in the product. Evaluating correlation among different parameters showed that, there were a positive significant correlation between HMF content with polyphenol compounds (r= 0.738), a* (r= 0.8868) and chroma index (r= 0.373) (p<0.05), and there were a negative significant correlation with brightness of appearance (r= -0.853) and hue angle (r= -0.858) of product at a level of 0.05. Also there were observed positive and significant correlation among polyphenol content of product with a* (r= 0.65) and chroma index (r= 0.298) and also negative and significant correlation with brightness (r= -0.655), hue angle (r= -0.651) and ph (r= -0.258). Therefore, honeyes with more redness and less brightness usually contain higher polyohenol which their participation in Millard reaction is the main reason for higher content of HMF in these samples. Therfore, determining suitable condition and storage time of honey according to their different primary characteristic should be considered in order to protect qualitative characteristic of product.