Methods and Importance of Food Evaluation

Every food item you pick up from a market shelf – whether it’s a packet of biscuits, a bottle of juice, or a bag of rice – has gone through some form of evaluation before it reached you. Food evaluation is the systematic process of analysing the nutritional content, safety, and overall quality of food products. It combines classical laboratory techniques with modern instrumental methods to measure proteins, fats, carbohydrates, vitamins, minerals, and other compounds present in what we eat. For food scientists, nutritionists, and regulatory bodies alike, these methods form the backbone of ensuring that our food supply remains safe, nutritious, and honestly labelled.

What is food evaluation? 🔗

Food evaluation refers to the assessment of food products for their chemical composition, nutritional value, sensory qualities, and safety. It answers fundamental questions: How much protein does this grain contain? Are there harmful contaminants in this vegetable? Does this packaged food match what its label claims?

The methods used in food evaluation range from simple chemical tests performed in basic laboratories to highly sophisticated instrumental analyses that can detect compounds at parts-per-billion levels. Food composition data produced through these methods are used extensively for nutritional analysis, prescription of therapeutic diets, nutrition labelling, research into diet-disease relationships, and national food and nutrition policy development . Without reliable food evaluation, none of these activities would be possible.

Proximate analysis: the foundation of food evaluation 🔗

Proximate analysis is the oldest and most widely used approach for determining the basic nutritional makeup of food. This system was originally developed in the mid-nineteenth century at the Weende Experiment Station in Germany to provide a broad classification of food components . Despite its age, it remains the first step in nearly every food evaluation process today.

The method breaks down food into six fundamental components:

Moisture (water content) – This is measured by weighing a food sample before and after drying it in an oven or through freeze-drying. Water content is one of the most variable components in food, especially in plant foods, and this variability directly affects the overall composition of the food . Fresh fruits, for example, may contain 80-90% water, while dried grains may have only 10-15%. Knowing moisture content is critical because it affects shelf life, texture, and how concentrated the other nutrients are.

Ash (mineral content) – When all organic matter in a food sample is burned away through incineration at high temperatures (around 500-600°C), what remains is the ash. This residue represents the total mineral content, including calcium, iron, potassium, sodium, and other inorganic elements. The purity and authenticity of a food sample can be assessed through total ash estimation, acid-insoluble ash, and water-soluble ash determinations .

Crude protein – Protein is typically estimated by measuring total nitrogen content using the Kjeldahl method, then multiplying by a conversion factor (commonly 6.25). This factor was originally based on the assumption that proteins contain 16 percent nitrogen, though it has since been refined with specific factors for different food categories . The newer Dumas combustion method provides a faster, automated alternative.

Crude fat – Fat content is determined through solvent extraction methods, where fats are dissolved using organic solvents like petroleum ether (the Soxhlet extraction method). The solvent is then evaporated, and the remaining fat residue is weighed.

Crude fibre – This represents the indigestible plant material remaining after treatment with dilute acid and alkali. Modern approaches have largely replaced crude fibre with dietary fibre measurements, which provide a more nutritionally meaningful value.

Nitrogen-free extract (NFE) – This is not measured directly. Instead, it is calculated by subtracting all the other components (moisture, ash, protein, fat, and fibre) from the total weight. NFE primarily represents sugars and starches.

Proximate analysis serves as a quality control measure ensuring the moisture content, protein, fat, fibre, carbohydrate, ash, and other components in food products meet regulatory compliance requirements . Standard methods for these analyses are published by organisations such as AOAC, FSSAI, BIS, and USDA.

Spectrophotometry: measuring nutrients with light 🔗

Spectrophotometry is a technique that uses light to identify and quantify specific compounds in food samples. The basic principle is straightforward: different molecules absorb light at characteristic wavelengths. By passing light of a specific wavelength through a food sample solution and measuring how much light is absorbed, scientists can determine the concentration of a particular nutrient.

This method is particularly useful for measuring vitamins, pigments, and antioxidants. For instance, vitamin C levels in citrus juice or the antioxidant capacity of a food product can be quickly assessed using UV-visible (UV-Vis) spectrophotometry. UV-Vis spectroscopy measures the absorbance of samples in the ultraviolet (250-400 nm) or visible (400-780 nm) spectrum, reflecting the energy absorbed during electronic transitions in molecules .

Advanced spectroscopic methods – including near-infrared (NIR), Raman, and fluorescence spectroscopy – provide rapid, non-destructive alternatives to traditional wet chemistry methods for food quality and safety assessment . NIR spectroscopy, for example, has become standard for analysing cereal grains because it can measure moisture, protein, and fat content simultaneously without destroying the sample.

The key advantages of spectrophotometric methods include relatively low cost, quick analysis time, and suitability for routine quality control in food manufacturing. Recent advances include portable instruments and handheld devices that allow faster quality analysis outside traditional laboratory settings .

Liquid chromatography: separating complex mixtures 🔗

Foods contain hundreds of different compounds mixed together, making individual nutrient measurement challenging. Liquid chromatography solves this problem by physically separating these compounds before measuring them individually.

The process works by dissolving a food sample in a liquid solvent (the mobile phase) and passing it through a column packed with special material (the stationary phase). Different compounds interact differently with the stationary phase, causing them to travel through the column at different speeds. As each compound exits the column separately, detectors identify and measure it.

High-Performance Liquid Chromatography (HPLC) is the most widely used form in food analysis. HPLC has become the preferred method for separating and measuring carotenoids, replacing older chromatographic methods that could only measure carotenes as a group . It is also the go-to technique for analysing water-soluble vitamins (like B-complex and vitamin C), amino acids, sugars, organic acids, and food additives.

HPLC systems equipped with mass spectrometric detectors are also widely used for protein identification through peptide mass fingerprinting . This level of detail is important for detecting allergens, verifying protein quality, and identifying food adulteration.

Fatty acid composition determination in food, which is essential for nutrition labelling and product development, is another key application of chromatographic techniques . Modern liquid chromatography systems can analyse dozens of compounds in a single run, making them indispensable in food laboratories worldwide.

Gas chromatography: analysing volatile compounds 🔗

Some food components – particularly those responsible for flavour and aroma – are volatile, meaning they evaporate easily at relatively low temperatures. Gas chromatography (GC) specialises in analysing these volatile compounds.

In GC, the food sample is first vaporised, then carried through a long, narrow column by an inert carrier gas (typically helium or nitrogen). As the vaporised sample moves through the column, different compounds interact with the stationary phase coating at different rates, causing them to separate and exit the column at distinct retention times .

Applications in food analysis 🔗

GC-MS (gas chromatography coupled with mass spectrometry) has been frequently used to detect the active compounds responsible for aroma and flavour in food, helping ensure quality and detect adulteration . For example, researchers have used GC-MS to identify over 100 volatile compounds in citrus fruits, characterising the chemical basis of their distinctive aromas.

Beyond flavour profiling, gas chromatography plays a vital role in determining fatty acid profiles in oils, fats, and dairy products, as well as detecting pesticide residues in fruits, vegetables, and grains . It can also analyse food additives, preservatives, and contaminants, making it a versatile tool in both quality assurance and food safety testing.

When combined with olfactometry (GC-O-MS), this technique can identify exactly which volatile compounds contribute most to a food’s perceived aroma, solving practical flavour problems in the food industry .

Food composition tables and databases 🔗

All the analytical methods described above feed data into a critical resource: food composition tables (FCTs) and food composition databases (FCDBs). These are comprehensive reference tools that list the nutritional content of hundreds or thousands of foods typically consumed in a country or region.

Food composition databases include detailed quantitative information on energy, macronutrients, micronutrients (vitamins and minerals), and other food components such as dietary fibre . They are maintained by national institutions – for example, the USDA’s FoodData Central in the United States, McCance and Widdowson’s dataset in the United Kingdom, and the FAO/INFOODS network at the international level.

Why food composition tables matter 🔗

Estimating nutrient intake from food consumption requires reliable data on food composition, and these data are also the foundation of food-based dietary guidelines for healthy nutrition . Without accurate FCTs, dietitians could not plan therapeutic diets, governments could not set nutrition policies, and researchers could not study links between diet and disease.

Here are the main areas where food composition data are essential:

Nutritional assessment – FCTs are needed to convert quantitative or semi-quantitative dietary data into energy and nutrient intakes . When a nutritionist records what a person eats, they use food composition data to calculate exactly how much protein, iron, vitamin A, or any other nutrient that person consumed.

Food distribution planning – Governments and international agencies like the WHO and FAO rely on food composition data to plan food aid, fortification programmes, and public distribution systems. Current food composition data are critically important for estimations related to nutrition and public health, food science and engineering, agrobiodiversity management, and food regulatory aspects .

Dietary counselling – Clinicians use food composition data to design personalised diets for patients with conditions like diabetes, kidney disease, or cardiovascular problems. Accuracy is especially vital when supporting vulnerable patients in clinical settings, where small differences in nutrient values could significantly impact their health .

Nutrition labelling – The nutritional information you see on packaged food labels is derived from food composition data, either through direct analysis or by using standard reference values from databases.

Research – Epidemiological studies investigating how diet affects health outcomes depend entirely on food composition data to quantify what populations are actually eating.

Challenges with food composition data 🔗

Regional differences in food composition arise from the use of local crop varieties, differing soil quality, and meteorological conditions, making cross-country comparability a persistent challenge . A tomato grown in India may have a different nutrient profile than one grown in Italy due to differences in soil, climate, and variety.

Nutrient content varies significantly across countries due to plant and animal varieties consumed, environmental conditions, and farming practices, which is why FCTs should ideally be developed at the country or regional level . Many developing countries still lack comprehensive, up-to-date food composition databases, which limits the accuracy of their nutrition programmes.

Why accurate food evaluation matters 🔗

Accurate food evaluation is not just an academic exercise – it has real-world consequences for public health, trade, and consumer protection.

Food safety – Analytical methods detect contaminants like pesticide residues, heavy metals, mycotoxins, and microbial toxins that can pose serious health risks. Regulatory agencies such as FSSAI in India, the FDA in the United States, and EFSA in Europe set maximum permissible limits for these contaminants, and enforcement depends on reliable testing.

Quality control in manufacturing – Food manufacturers use proximate analysis and instrumental methods to ensure every batch of their product meets the composition stated on the label. A protein bar that claims 20 grams of protein per serving must be verified through nitrogen analysis.

Preventing food fraud – Sophisticated chromatographic and spectroscopic methods can detect adulteration. For example, HPLC can identify if olive oil has been mixed with cheaper vegetable oils, and GC can detect synthetic flavour compounds passed off as natural ones.

Supporting nutrition interventions – Food composition tables also provide information on chemical forms of nutrients and the presence of interacting components, which helps assess bioavailability – how much of a nutrient the body can actually absorb and use . This is critical for designing effective fortification programmes in regions facing micronutrient deficiencies.

Emerging trends in food evaluation 🔗

Food evaluation is not standing still. Several new technologies are reshaping how we analyse food:

Rapid and non-destructive testing – Spectroscopic methods like hyperspectral imaging, Raman spectroscopy, and NIR offer rapid, non-destructive alternatives that avoid the laborious, time-consuming, and expensive processes of traditional analytical techniques . Portable versions of these instruments are already being used for on-site quality checks in fields, warehouses, and food processing plants.

Biosensors – These devices use biological recognition elements (like enzymes or antibodies) to detect specific compounds quickly and at low cost. They hold promise for real-time monitoring during food production.

AI and machine learning – Chemometric approaches, including prediction models like PLS regression, support vector machines, and artificial neural networks, are increasingly used to analyse spectroscopic data and predict chemical and physical properties of food . These computational tools are making data from advanced instruments more useful and accessible.

Two-dimensional chromatography (GC×GC) – This technique uses two columns with different separation mechanisms, providing far greater resolution for analysing extremely complex food samples with hundreds of volatile compounds.

Bringing it all together 🔗

Food evaluation is a multi-layered process. Proximate analysis provides the big picture – how much protein, fat, carbohydrate, and moisture a food contains. Spectrophotometry adds detail by measuring specific vitamins, pigments, and antioxidants. Liquid chromatography separates and quantifies individual amino acids, sugars, and vitamins with high precision. Gas chromatography handles the volatile world of flavours, aromas, and fatty acids. And all this data ultimately flows into food composition tables that serve as the foundation for nutrition science, public health policy, and dietary guidance worldwide.

Without these methods working together, we would have no reliable way to know what is in our food, whether it is safe, or whether it provides the nutrition we need. As analytical technology continues to advance, food evaluation will only become more precise, faster, and more accessible – benefiting consumers, producers, and policymakers alike.

What do you think? How much do you trust the nutritional information printed on packaged food labels, and do you believe developing countries should invest more in building their own food composition databases rather than relying on international data?

References

1. https://www.fao.org/4/y4705e/y4705e12.htm
2. https://fdc.nal.usda.gov/
3. https://www.fao.org/infoods/infoods/en/
4. https://www.fssai.gov.in/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC7582643/