FST 302 — Basic Food Chemistry: Lecture Note

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LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: FST302 Course title: Basic Food Chemistry Course credit load: 2 units List of Series: 1. Principles of Proximate Analysis in Food Chemistry 2. Determination of Food Constituents and Contaminants 3. Protein Analysis Methods Beyond Kjeldahl 4. Characterization of Free and Bound Lipids 5. Sugar Determination Techniques: Lane & Eynon, Munson & Walker, and Dubois Methods Part 1: Foundations of Proximate Analysis • Sub-Part 1.1: Definition and Scope of Proximate Analysis • Sub-Part 1.2: Importance of Proximate Analysis in Food Chemistry • Sub-Part 1.3: General Methods and Principles Part 2: Moisture and Ash Determination • Sub-Part 2.1: Methods of Moisture Analysis • Sub-Part 2.2: Methods of Ash Analysis Part 3: Crude Protein and Crude Fat Determination • Sub-Part 3.1: Principles of Protein Analysis (including Kjeldahl overview) • Sub-Part 3.2: Methods of Crude Fat Analysis Part 4: Crude Fibre and Carbohydrate Determination • Sub-Part 4.1: Methods of Crude Fibre Analysis • Sub-Part 4.2: Determination of Total Carbohydrate Introduction Food is central to human survival, yet the quality and safety of what we consume depend greatly on knowing its composition. Imagine standing in a food laboratory, faced with a sample of flour or milk, and being asked to determine how much protein, fat, fibre, or carbohydrate it contains. This is where proximate analysis becomes essential. It provides the basic chemical breakdown of food, offering a foundation for nutrition studies, food processing, and quality control. In this Series,

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS you will be guided through the principles and applications of proximate analysis, which form the bedrock of food chemistry. The aim of this Series is to equip you with the knowledge and skills to explain, apply, and evaluate the methods used in proximate analysis, enabling you to interpret food composition data with confidence. We shall commence this Series by examining the foundations of proximate analysis, including its definition, scope, and importance. Next, we will move on to the determination of moisture and ash, which are critical indicators of food stability and mineral content. Following that, we will explore the analysis of crude protein and crude fat, focusing on their principles and laboratory methods. Finally, we will wrap up by studying crude fibre and carbohydrate determination, thereby completing the full spectrum of proximate analysis techniques. This sequential journey will provide you with a comprehensive understanding of how food composition is scientifically assessed. Series Learning Outcomes Upon completing this Series, you should be able to: SLO 1.1 define the concept and scope of proximate analysis in food chemistry, SLO 1.2 explain the importance and general principles underlying proximate analysis, SLO 1.3 demonstrate methods for determining moisture content in food samples, SLO 1.4 apply techniques for analysing ash content as a measure of mineral composition, SLO 1.5 describe the principles of crude protein determination with reference to the Kjeldahl method, SLO 1.6 perform crude fat analysis using standard laboratory procedures, SLO 1.7 analyse crude fibre content in food samples, and SLO 1.8 evaluate carbohydrate composition through proximate analysis methods. 1.1 Foundations of Proximate Analysis 1.1.1 Definition and scope of proximate analysis Proximate analysis is the classical method used to determine the basic chemical composition of food. It involves the estimation of six major components: moisture, ash, crude protein, crude fat, crude fibre, and carbohydrate. These are referred to as the proximate principles because they provide a broad overview of the nutritional value of food. The scope of proximate analysis is wide, ranging from food quality control to nutritional evaluation and regulatory compliance. For

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS example, food industries rely on proximate analysis to ensure that their products meet labelling requirements, while nutritionists use it to assess dietary intake. In research, proximate analysis serves as a baseline for more advanced studies on food chemistry. By breaking food down into these six components, proximate analysis allows scientists and technologists to make informed decisions about processing, preservation, and consumption. It is often the first step in food analysis because it provides a rapid and reliable estimate of composition. Fill in the blank: Proximate analysis provides information about the ______ composition of food. Figure 1.1 Components of proximate analysis in food chemistry 1.1.2 Importance of proximate analysis in food chemistry The importance of proximate analysis lies in its ability to provide essential data for food evaluation. For instance, the moisture content of food is directly related to its shelf life and susceptibility to microbial growth. Foods with high moisture content, such as fresh fruits, are more prone to spoilage, whereas low-moisture foods like cereals are more stable. The ash content of food reflects its mineral composition, which is vital for human health. Minerals such as calcium, iron, and zinc are critical for physiological functions, and their levels can be inferred from ash analysis. Crude protein and crude fat are macronutrients that determine the energy and nutritional value of food. Protein is essential for growth and repair of tissues, while fat provides concentrated energy and aids in the absorption of fat-soluble vitamins. Crude fibre plays a role in digestion and bowel health, and carbohydrate is the primary source of energy for the body. Together, these proximate principles provide a comprehensive picture of food quality.

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS In food industries, proximate analysis is indispensable for product development, quality assurance, and compliance with nutritional labelling standards. For consumers, the values derived from proximate analysis help in making informed dietary choices. Fill in the blank: The proximate principle that indicates the mineral composition of food is called ______. Box 1.1 Selected applications of proximate analysis 1.1.3 General methods and principles The methods of proximate analysis are based on fundamental principles of gravimetric analysis, which involves measuring changes in weight, and volumetric analysis, which involves titration and measurement of liquid volumes. For example, moisture is determined by drying food samples to constant weight, often using an oven or vacuum drying technique. Ash is obtained by incinerating food at high temperatures in a muffle furnace until all organic matter is burnt off, leaving only the mineral residue. Protein is commonly measured using the Kjeldahl method, which estimates nitrogen content. This method involves digestion of the food sample with concentrated sulphuric acid, conversion of nitrogen into ammonium sulphate, and subsequent distillation and titration to determine nitrogen levels. Fat is extracted using solvents such as ether or petroleum spirit in a Soxhlet apparatus, which allows continuous extraction until all fat is removed. Fibre is determined by sequential digestion with acid and alkali to simulate the digestive process, leaving behind indigestible residue. Carbohydrate is usually calculated by difference, subtracting the sum of moisture, ash, protein, fat, and fibre from 100. These methods are standardised to ensure reproducibility and accuracy. They provide a reliable framework for food analysis, although modern techniques such as chromatography and spectroscopy are increasingly used to complement proximate analysis. Fill in the blank: The method commonly used to estimate protein content in food is the ______ method.

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Table 1.1 Overview of proximate analysis methods Pilot questions 1.1 1. Which term refers to the systematic determination of food composition into six basic components? 2. What proximate principle is used to estimate the mineral content of food? 3. Which method is commonly applied to determine protein content in food samples? 4. Why is moisture content important in food chemistry? 5. What analytical approach involves measuring weight changes in food samples?

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.2 Moisture and Ash Determination 1.2.1 Methods of moisture analysis Moisture content refers to the amount of water present in a food sample. It is a critical factor because it influences the shelf life, texture, and microbial stability of food. Foods with high moisture content, such as fruits and vegetables, are more prone to spoilage, while low-moisture foods like cereals and powdered milk are more stable. Determining moisture is therefore essential for food preservation and quality control. The most common method of moisture determination is oven drying, where a food sample is heated at a controlled temperature until it reaches constant weight. This method is simple and widely used, but care must be taken to avoid decomposition of heat-sensitive components. Another approach is vacuum oven drying, which reduces the risk of thermal degradation by lowering the pressure and drying at lower temperatures. Distillation methods, such as the Karl Fischer titration, are also employed for precise measurement, especially in foods with volatile compounds. Fill in the blank: The most common method of moisture determination in food is ______ drying. Figure 1.2 Oven drying method for moisture analysis Moisture analysis is not only important for food safety but also for economic reasons. For example, excessive moisture in flour can reduce its

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