EFFECT OF PRETREATMENTS AND DRYING METHODS ON THE PHYSICOCHEMICAL AND ANTIOXIDANT PROPERTIES OF EGGPLANT (SOLANUM AETHIOPICUM) FLOUR

1.1 Background of the Study 

1.2 Statement of the Problem

1.3 Justification of the Study

1.4 Objectives of the Study 

2.1 Vegetables

2.2 Relevance of Vegetables in Human Health

2.3 Postharvest Losses of Vegetables 

2.4 Description of Eggplant

2.4.1 Nutritional Content and Health Benefits of Eggplant

2.4.2 Processing and Utilization of Eggplant 

2.4.3 Antioxidant Capacity of Eggplant

2.5 Pretreatment of Vegetables 

2.5.1 Physical Pretreatment

2.5.1.1 Thermal Blanching

2.5.1.2 Non-Thermal Process

2.5.2 Chemical Pretreatment

2.6 Drying of Vegetables 

2.6.1 Methods of Drying 

2.6.1.1 Osmotic Dehydration 

2.6.1.2 Solar Drying 

2.6.1.3 Hot Air Convective Drying 

2.6.1.4 Spray Drying 

2.6.1.5 Microwave Drying 

2.6.1.6 Infrared Drying 

2.6.1.7 Sun Drying

2.7 Antioxidants 

2.7.1mechanism of Action of Antioxidants 

3.1 Source of Raw Materials

3.2 Samples Preparation

3.2.1 Method of Treatment and Production

3.2.2 Procedures for Blanched, Oven and Sun Drying Of Eggplants

3.2.3 Procedures of Citric Acid, Oven and Sun Drying Of Eggplants

3.3 Method of Analyses

3.3.1 Proximate Analysis of the Dehydrated Eggplant

3.3.1.1 Moisture Determination

3.3.1.2 Determination of Crude Protein

3.3.1.3 Crude Fiber Determination

3.3.1.4 Ash Content Determination

3.3.1.5 Determination of Fat Content

3.3.1.6 Total Carbohydrate Determination

3.3.2 Minerals Determination of the Eggplant Flours

3.3.3 Vitamins Determination of the Eggplant Flours

3.3.4 Determination of Functional Properties of Eggplant Flours

3.3.4.1 Swelling Power Index Determination 

3.3.4.3 Water Absorption Capacity (WAC) Determination

3.3.4.4 Oil Absorption Capacity (OAC) Determination

3.3.4.5 Wettability Determination

3.3.5 Determination of Antioxidant Properties and Activity of the Eggplant Flours

3.3.5.1 Total Polyphenol Determination

3.3.5.2 Total Flavonoid Determination

3.3.5.3 Determination of DPPH Radical Scavenging Activity

3.3.5.4 Determination of ABTS Radical Scavenging Activity

3.3.5.5 Determination of Frap

3.4 Experimental Design

3.5 Statistical Analysis

4.1 Pretreated and Dried Eggplant Flour Samples

4.2 Proximate Composition of Eggplant Flour Samples

4.3 Minerals Composition of Eggplant Flour Samples

4.4 Vitamins Composition of Eggplant Flour Samples

4.5 Functional Properties of Eggplant Flour Samples

4.6 Antioxidant Properties and Activities of the Eggplant Flour Samples    

4.7 Pearson Correlation Coefficient of Total Polyphenol, Flavonoids, Vitamin C

5.1 Conclusion

5.2 Recommendations

References

Table 4.2 Proximate Composition of Eggplant Flour Samples

Table 4.3 Minerals Composition of Eggplant Flour Samples

Table 4.4 Vitamins Composition of Eggplant Flour Samples

Table 4.5 Functional Properties of Eggplant Flour Samples

Table 4.6 Antioxidant Properties and Activities of Eggplant Flours And Antioxidant Activity of Eggplant Flours

Figure 1: Flow Chart For Production Of Blanched Oven And Sun Dried Eggplant Flour As Described By Eneche, (2006).

Figure 2: Flow Chart For Production Of Citric Acid Oven And Sun Dried Eggplant Flour As Described By Eneche, (2006).

Plate1:  Whole and Sliced Eggplant

Plate 2: Pretreated and Dried Eggplant Flours                                          

Vegetables play vital role in human nutrition. Each vegetable contain a unique amount of various nutrients that are strongly linked with the protection of different health diseases (Naeem and Ugur, 2019). According to Dias (2012), vegetable provide micronutrients, dietary fiber, and phytochemicals that are associated with improvement of gastrointestinal health, good vision, and reduced risk of heart disease, stroke, chronic diseases like diabetes, and some forms of cancer. 

Eggplant (Solanum aethiopicum) is vegetable crop with coarsely lobed leaves (Naeem and Ugur, 2019). It is an integral part of African tradition and diet known as ‘gauta’ or ‘yalo’, by the Hausas, ‘afufa’ or ‘anara’ in Igbo and ‘igba’ in Yoruba (Chinedu et al., 2011). Eggplants possess 4.58 to 5.79 % protein, 1.65 to 2.13 % lipid, 1.78 to 1.81 % crude fibre and 11.77 to 15.42 % carbohydrate (Agoreyo et al., 2012). It is one of the best dietary sources of biologically active polyphenolic compounds, vitamins, antioxidants and medicinal requirements (Sohani and Tawar, 2019). Eggplants possess appreciable phytochemical substance like anthocyanin (Sanchez-Mata et al., 2010). It is reported to have analgesic, antipyretic, antioxidant, anti-inflammatory, anti-asthmatic, hypo-lipidemic, anti-platelet and anaphylactic reaction inhibitory activities (Solanke and Tawar, 2019).

Fresh vegetables like eggplant are perishable and difficult to preserve due to their high moisture content and tender texture (Deng et al., 2017). Drying is one of the most common preservation methods for extending the shelf life of vegetables by reducing the water content to a level so as to prevent the growth and reproduction of microorganisms and to inactivate many of the moisture-mediated deteriorative reactions (Mujumdar, 2014; Omolola et al., 2017). Drying extensively reduces the weight and volume of vegetables and brings benefits like minimizing packing, storage and transportation costs (Kamiloglu et al., 2016). Vegetables are usually subjected to physical or chemical pretreatment before drying to shorten the drying time, reduce the energy consumption and preserve the quality of products (Yu et al., 2017). 

Hot water blanching is a common pretreatment used prior to drying. It involves immersion of fresh products like vegetables into hot water at temperatures of 95°C for 3-5 minutes (Guida et al., 2013). Hot water blanching helps to accelerate drying rate by changing the permeability of the vegetable’s cell membranes (Jangam, 2011). Citric acid has been confirmed to accelerate the drying process (Hiranvarachat et al., 2011). The effects of citric acid pretreatment on maintaining colour and enhancing drying rate of vegetables is influenced by the concentration of solution, dipping time and temperature (Deng et al., 2017).

Antioxidant is a substance that is capable of slowing down the autoxidation process of other compounds or neutralize freeradicals (Kebede and Admassu, 2019).Vegetables are the richest sources of antioxidant compounds like ß-carotene, vitamins A, C and E (Kebede and Admassu, 2019) of which most of them have been investigated for the prevention of diseases such as cancer and coronary heart disease (Yadav et al., 2016). This study therefore focuses on evaluating the effect of pre-treatments and drying on the physicochemical and antioxidants properties of dehydrated eggplant slices. 

The provision of adequate and affordable food for all is the fundamental basis for food security. Although there is remarkable progress made in increasing food production worldwide, a good number of the populations in developing countries do not have access to adequate food supplies due to factors such as postharvest losses. Eggplant like most other vegetables are seasonal and highly perishable especially during peak harvesting season due to factors like moisture content, respiratory rate, ethylene production, endogenous plant hormones and exogenous factors such as microbial growth, temperature, relative humidity and atmospheric compositions (Yahaya and Mardiyya, 2019). In Nigeria, many varieties of eggplant are produced yearly without any preservation and end-product uses. This results to postharvest losses to farmers and attendant high rate of food insecurity. Attempt to produce eggplant flour will go a long way to prevent postharvest losses for functional end uses. Aside this, there is dearth of information in literature on the effect of pre-treatments and drying on the physicochemical and antioxidants properties of eggplant flour.

The present study will reveal the pre-treatment method that its quality attributes like nutrient composition is higher. This will aid to ensure that consumers use appropriate pre-treatment method in processing egg plants in other to obtain adequate nutritional value of eggplant. More so, dehydration of eggplant will contribute in reducing their post-harvest losses thereby contributing to food security. The findings of this study will be of immense benefit to vegetable processing industries in addition to stimulating more research in minimizing postharvest losses of vegetables in Nigeria.

The main objective of this study was to evaluate the effect of pre-treatments and drying on the physicochemical and antioxidants properties of eggplant flour.

The specific objectives were to: