The effect of different drying conditions and methods on antioxidant properties and the amount of phenolic compounds in olive leaves

Dissertation for Master's Degree

Food Technology Orientation

Persian abstract

Background and purpose:

Olive tree leaves have many compounds including Oleuropein is the main medicinal properties related to it. Olive leaf extract is also rich in phenolic compounds. In order to extract phenolic compounds, olive leaves must first be dried. Natural drying and hot air drying are the most important methods used in the production of dried plant material. Another method of drying is using a microwave. The high speed of drying of new energy rhodic prevents the reduction of the essence. This study was carried out in order to determine the best drying method according to the different methods of drying olive leaves with the highest physico-chemical characteristics and acceptable effective substances. Materials and methods: In this study, olive leaves were dried in three ways after collection. In the first group, olive leaves were dried in the oven (at 3 different temperatures). In the second group, the leaves were dried in a fluid bed dryer (at 3 different temperatures) and in the third group, the leaves were dried using a combination method of oven-microwave and fluid bed-microwave.

After drying the leaves, the amount of phenolic compounds and DPPH free radical inhibition were evaluated and compared in the laboratory in each of the methods used, and the best drying method was determined based on the extraction of antioxidant and phenolic compounds present in the dried leaves. Also, in this research, the image processing method was used to investigate color changes during drying.

Findings:

In this study, the results of the experiments showed that the use of microwaves can increase the survival of phenolic compounds and inhibit DPPH free radicals. But with increasing dryer temperature and microwave power, this amount decreases. So that the lowest amount of phenolic compounds and inhibition of DPPH free radical in different treatments was related to the temperature of 75°C and the highest was related to the temperature of 35°C. Also, in the treatments where microwave was used, the amount of phenolic compounds and inhibition of DPPH free radical was more than in the case where microwave was not used, but with the increase of microwave power from 360 to 720 watts, this amount decreased.

The results of image processing showed that with increasing dryer temperature and microwave power, the amount of leaf color degradation increases. For example, the lowest value of the L index was related to the temperature of 35 degrees Celsius and without microwave pretreatment, and the highest value was related to the temperature of 75 degrees Celsius and the power of 720. The changes in index b were also the same as index L, but index a was the opposite of the previous two indices, so that this index was the highest at 35 degrees Celsius without microwave pretreatment, and its lowest temperature was at 75 degrees Celsius and 720 power. Discussion: The reason for reducing the amount of phenolic compounds and inhibiting the DPPH free radical by increasing the dryer temperature and microwave power It can be attributed to the loss of phenolic compounds as well as the removal of these compounds from the organs during drying.

The cause of the increase in leaf color degradation with increasing drying temperature and microwave power is related to the sensitivity of olive leaf pigments to high powers and temperatures.

Keywords: olive leaf, drying, phenolic compounds, antioxidant compounds, image processing

Chapter One

Introduction and Generalities

1-1-olive

Olive (Olea europaer) is a shrub of the Oleaceae family with evergreen leaves, which in its wild state has a height of about 5 meters or a little more, but if grown in favorable conditions, its height reaches 12 to 15 meters and its trunk circumference reaches 3 to 4 meters.It is widely distributed in the Mediterranean Sea, North Africa, Southeast Asia, North-South China, Scotland and Eastern Australia (Malek, 2015; Maqsoudi, 2015).

1-2- Its special features

Olive leaves have a reciprocal position on the stem and a long oval appearance, pointed, leathery in light green color and beautiful, wide on the upper surface, but the lower surface of the pan has a lighter color (Zargari, 1369). Olive tree bark and leaves have bitter taste and diuretic, tonic, astringent, febrifuge and blood pressure lowering effect. The last two properties are mostly found in olive leaves (Zarzello, 1991). Olive leaves contain compounds Phenolic, terpene compounds, fat-soluble compounds (squalane, beta-carotene, alpha-copherol, beta-sitosterol, linear alcohols, alpha-amidine, beta-amidino), carbohydrates, acids Amine, vitamins, minerals. (Govinda, 2006). Zytonia leaves are one of the most abundant sources of polyphenols among plants, and the phenolic compound faraventhrin is present in it, and most of its medicinal properties are related to it (Lojanohamkaran, 2006).

The results of some researches show that the presence of phenolic compounds in the extracts of these leaves has antimicrobial, antifungal, and antifungal effects (Govinda, 2006).

1-3-polyphenols

Polyphenols are one of the most abundant metabolites of plants and are considered inseparable components of human and animal diets. In recent decades, polyphenolic compounds have found a special place in the food and pharmaceutical industries (Manach et al., 2004; Escalbertohmkaran, 2005). Polyphenols have aromatic benzoic (phenyl) ring and hydroxyl (OH) group in their chemical structure. Polyphenols are divided into several groups such as: anthocyanidins, Catechins, flavanones, flavones, flavonols, isoflavones, hydroxybenzoic acids, hydroxycinnamic acids, lignans, tannins or proanthocyanidins (Fangobandari, 2010). Table 1-1 contains some examples of the main polyphenols along with their plant sources and some of their chemical properties.

rtl;"> Among the beneficial biological properties of these compounds, their antimicrobial, antiviral, antioxidant and anti-inflammatory effects can be indicated (Benik, 2002; Haslam, 1996; Koideo and Feldman, 1996).

1-4- Extraction of phenolic compounds

The ancient techniques of extracting herbal materials with solutions were mainly based on the correct selection of solvents and the use of heating and cooling that improve charge transfer. These methods include: immersion method, Soxhle method and percolation with hot water-alkaline-fat mixture. In these methods, herbal materials are placed in contact with the solvent for a certain period of time, and the compounds in question are dissolved and extracted (Wangwoler, 2006). One of the innovative methods of extracting herbal extracts is extraction using microwaves. Reduction of extraction time, smooth operation, accurate monitoring of the reaction by temperature and pressure sensors, automation, uniform heating and low solvent consumption are among the advantages. Extraction with microwaves are considered to be synthetic methods (Jinohhamkaran, 2009). In fact, drying is one of the topics that has had the most studies in food engineering so far (Rathi, 2009).

The basis of the drying process is the reduction of water, or in other words, water activity, which leads to the prevention of microbial, chemical and biochemical spoilage and the increase of the shelf life of the product.

The different stages of the general curves of food drying are: From: (Figure 1-1)

1- Initial adaptation period: a short-term period when the materials reach equilibrium with the drying conditions. (Part AB)

2- Constant speed period[1]: The drying speed is constant during this period. And the moisture content decreases linearly with time. In other words, the rate of moisture evaporation is equal to the rate of moisture transfer from the central parts to the surface of the solid material and continues until the critical moisture content is reached.

The transfer phenomenon in this period includes the transfer of water vapor mass from the surface of the material by an air layer to the environment, as well as the transfer of heat by food solids.

During this period, the two main mechanisms of capillary flow and molecular diffusion are the two internal transfer mechanisms. are considered humidity. (Part BC)