1.1. Nutraceuticals

Nutraceuticals are natural food products that have health benefits, such as improving physiological function and treating a variety of illnesses. Products made from isolated nutrients, dietary supplements, genetically modified designer foods, herbal items, processed foods, and drinks are included in the category of nutraceuticals. Functional foods with probiotic benefits include fresh foods, such as fruits, vegetables, and fermented meals containing living organisms, as well as “vitamin-enriched” health-promoting products. Nutraceuticals offer a proactive healthcare approach with significant therapeutic effects on the human body. With pharmaceutical dosage forms (pills, powders, capsules, etc.) that contain food bioactive substances as active ingredients, nutraceuticals are a major development in healthcare medicine linked to food science. They include a variety of products derived from isolated nutrients, dietary supplements, and genetically engineered designer foods, herbal products, processed foods, and beverages. Among them, “vitamin-enriched” health-promoting products and also fresh foods, such as vegetables, fruits, and fermented foods populated with live cultures, are considered to be functional foods with probiotic benefits. Thus, nutraceuticals provide a proactive healthcare approach with tremendous therapeutic impact on the human body (Bagchi et al., 2015; Das et al., 2012).

1.2. Malnutrition

Malnutrition is a serious global health issue and a major cause of death in low-income and developing nations. In particular, malnutrition and undernutrition (mostly of proteins and micronutrients) are recognized as major public health concerns in a number of regions of the world (Million et al., 2017). In this context, methods for preventing and treating malnutrition have been identified, including food diversification, food fortification, biofortification, and food supplementation. Food supplementation and fortification have been employed for a long period as economical means to combat malnutrition, particularly in Third World nations (Ohanenye et al., 2021).

1.3. Role of Nutraceuticals in prevention of disease

Nutraceuticals are used to enhance health, delay the aging process and lengthen life expectancy, prevent chronic diseases, and simply sustain the body’s integrity and functions. These products are regarded as a beneficial resource for preventing illnesses, such as diabetes, kidney and gastrointestinal problems, and various infections. Numerous nutraceuticals have important roles in immune functioning and vulnerability to specific diseased states. Additionally, oxidative stress-related disease-modifying indications for nutraceuticals include cancer, Alzheimer’s disease, cardiovascular diseases, allergies, eye disorders, Parkinson’s disease, and obesity.

2.1. Antioxidants

Functional foods that are high in antioxidants, such fruits, vegetables, and nuts, are essential for reducing the negative effects of dangerous free radicals in the human body (Stephen et al., 2023). Antioxidants play a key role in scavenging these free radicals, a procedure that has serious health consequences. Antioxidants are widely acknowledged for their capacity to reduce inflammation and oxidative stress, and play a significant role in preventing chronic illnesses (Vignesh et al., 2022). Antioxidants have the ability to counteract the variables that contribute to cardiovascular diseases; thus their significance in cardiovascular health is particularly notable (Wang & Kang, 2020). These substances support the preservation of vascular health and general cardiovascular well-being by lowering oxidative stress.

2.2. Omega-3 fatty acid

Omega-3 fatty acids are essential components of functional foods known for their dual effects on cardiovascular and cognitive health. They are found in large quantities in foods such as walnuts, flaxseeds, and fatty fish (Fekete et al., 2023). Alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) are the three main constituents of omega-3 fatty acids. Only diet can provide ALA, the parent omega-3 fatty acid family, which subsequently is transformed into EPA and DHA. This conversion mechanism, however, is insufficiently effective in humans to meet the requirement of EPA and DHA, both involved in positive health effects (Siriwardhana et al., 2012).

2.3. Lignan and soluble fiber

Lignans are phytoestrogens abundantly available in fiber-rich plants, cereals (wheat, barley, and oats), legumes (bean, lentil, and soybean), vegetables (broccoli, garlic, asparagus, and carrot) fruits, berries, tea, and alcoholic beverages. Flaxseeds contain about 75–800 times more lignans than cereal grains, legumes, fruits, and vegetables (Meagher & Beecher, 2000). Flaxseeds serve as a good source of both soluble and insoluble dietary fiber. Flaxseed mucilage has gained momentum due to its superb health benefits and potential functional properties (Susheelamma, 1987).

Nutraceuticals are the products that primarily aim to grant health benefits much more than what is achieved by normal foods and diets. Nutraceuticals available in the market today are classified into numerous broad categories based on their origin, function, and regulatory standards. These mainly consist of functional foods, dietary supplements, and medical foods (AlAli et al., 2021). Each category offers different functions, that is, adding specific nutrition for curing a particular ailment. Table 1 summarizes few sources of nutraceutical products along with their health benefits.

3.1. Functional Foods

Functional foods are the food products that, in addition to providing essential nutrients, have specific compounds or components beneficial to health and conducive to the reduction of disease(s). This may consist of vitamins, minerals, dietary fibers, probiotics, antioxidants, and different bioactive compounds. Functional foods are usually whole or minimally processed, but they can also be fortified with additional nutrients (Obayomi et al., 2024). Functional foods can be distinguished from conventional food by its specific health target(s) with scientific evidence to support it. Functional foods were first introduced in Japan in the 1980s, as an element of “Foods for Specified Health Use” (FOSHU) and defined as foods with health benefits beyond basic nutrition. Since the daisy chain effect in functional foods started, it is now routinely employed globally but with country-based definitions and regulations (Sun-Waterhouse, 2011).

Functional foods have shown a number of health benefits. Their regular consumption reduces the risk of chronic diseases, cardiovascular diseases, diabetes, and some cancers. Functional foods are rich in antioxidants, including vitamin C, polyphenols and beta-carotene, that reduce oxidative stress involved in aging and the development of a disease. Healthy fats, such as omega-3 fatty acids from fish and flaxseeds, contribute to a healthy body by reducing inflammation that helps both heart and brain (Essa et al., 2023). Probiotics in fermented food balance gut microbiome, boost immunity, help with digestive issues, and even help in proper functioning of the gut–brain axis (Hemarajata & Versalovic, 2013).

Demand of functional foods has increased due to consumer interest and ability of the food industry to innovate more functional food products for desired health action. One avenue of development is the incorporation of bioactive compounds, such as curcumin, resveratrol, and plant sterols into functional foods. High performance in bioactivity of such natural compounds is commonly limited by their stability, bioavailability, and efficacy because of food processing conditions and changes during storage (Obayomi et al., 2024). Functional foods assert scientific verification to avoid exaggeration to customers.

Countries have different regulations about governing functional food norms, being stricter in the European Union and Japan and more relaxed in other areas. In the United States, functional foods are classified as dietary supplements under the jurisdiction of the US Food and Drug Administration (US FDA), but not requiring the same regulatory scrutiny as expected for pharmaceuticals (Farid et al., 2019).

3.2. Dietary Supplements

Dietary supplements are the preparations that supply nutrients or other bioactive compounds that may be missing in daily diet. These are vitamins, minerals, amino acids, enzymes, probiotics, antioxidants, and botanicals designed to help the body to maintain health or assist with a specific nutritional requirement. While supplements may benefit the overall well-being, most are designed to prevent nutrient deficits; improve immunity; promote exercise performance and recovery; and provide routine functions for physiological processes in both military and nonmilitary populations identified as being at increased risk of nutritional deficits or requiring specific medical requirements (Shao et al., 2021).

The most widespread dietary supplements are vitamins (e.g., vitamins A, C, D, E, and K as well as the vitamin B complex) and minerals (e.g., calcium, magnesium, iron, and zinc). These include important nutrients for energy, immunity, bone health and production of red blood cells (RBCs) (Mishra et al., 2021). For example, vitamin D and calcium are commonly recommended as nutritional supplements in the treatment/prevention of osteoporosis, particularly in the older population. Iron is involved with oxygen transport and prescribed to prevent anemia in menstruating women and to those with low bioavailable iron dietary intake (Godswill et al., 2020).

Herbal supplements are the concentrated forms of specially selected beneficial compounds derived from plants, including herbs, roots, and flowers. Some common examples are echinacea to support the immune system, ginseng to provide energy, and turmeric (curcumin) for anti-inflammatory effects. Such supplements are used in traditional medicine and studied for their therapeutic effects (Mercola, 2021). Amino acids form protein and are essential for muscle recovery, activity of neurotransmitters, and metabolic health. Branched-chain amino acids (BCAAs) work well for recovery and performance of muscles and are therefore commonly used by athletes; specific amino acids, such as glutamine, support immune function and cell division; and lysine provides structural support to connective tissues (Rajendram et al., 2015).

Omega-3 fatty acids found in fish oil and in plants, such as flaxseeds, are essential for normal cardiovascular, cognitive, and inflammatory physiology. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplements are commonly used for reducing triglycerides and supporting mental health, especially in those who do not consume enough of fatty fish (Laye et al., 2018). On the other hand, probiotics are live beneficial bacteria or yeast that help to improve the microbiome and thus support gut health. They are essential for those with digestive problems, such as irritable bowel syndrome, and for general immune support, given the importance of gut microbiome in immune homeostasis (Sánchez et al., 2017).

Dietary supplements work differently in the body depending on the compounds included. Vitamins and minerals in common act as cofactors to enzymatic reactions demanded for cellular processes (Mishra et al., 2021). The bioactivity of herbal supplements is associated with antioxidant, anti-inflammatory, or adaptogenic effects by modulating several biological pathways. Amino acids are the foundational building blocks of proteins and thus assist in the repair and maintenance of the cells, while probiotics function by balancing gut microflora composition and improving gut barrier integrity (Mercola, 2021).

3.3. Medical Foods

Medical foods are governed by the US FDA under the Orphan Drug Act. They are structured to have either enteral ingestion or enteral application under the guidance of a clinician (Holmes et al., 2021). Medical foods differ from traditional foods, as the former are designed and prescribed for specific nutritional needs of patients with distinctive metabolic or physiological requirements because of a disease. They are not ordinary foods that contribute to the overall nutrition, or drugs designed to cure or treat a disease (Mozaffarian et al., 2024).

Medical foods are prescribed for treating various chronic and acute conditions, including metabolic disorders, neurologic condition, gastrointestinal disorders, and malnutrition. To illustrate, people with phenylketonuria (PKU), a genetic condition that restricts how the body metabolizes phenylalanine, (an amino acid found in high-protein foods), will frequently need medical food which are free of phenylalanine (McWhorter et al., 2022). In a similar context, for patients with Alzheimer’s disease it is suggested that ketone-precursor-enriched medical food can supply an alternative brain fuel source to ameliorate cognitive deficits linked to impaired glucose metabolism (Taylor et al., 2019).

3.4. Probiotics and Prebiotics

Prebiotics and probiotics are the functional foods or supplements that are beneficial for gut health components that add to microbiome balance and optimal health via the gut–brain axis (Dahiya & Nigam, 2022).

Probiotics are live bacteria or yeast that may provide health benefits if prescribed in adequate quantity. Lactobacillus, Bifidobacterium, and Saccharomyces boulardii are some of the common probiotic strains. These good microbes are present in different fermented foods, such as yogurt, kefir, sauerkraut, kimchi, and some supplements. They colonize the gastrointestinal tract, combat pathogenic bacteria, and provide protection to gut barrier, thus preventing infections and related diseases (Ansari et al., 2023). Probiotics are effective when they colonize in the gut with suppressing effect through competition against others. They also generate short-chain fatty acids (SCFAs), including acetate, butyrate, and propionate, which nourish colon cells, suppress inflammation, and help to ensure that gut barrier stays intact. Moreover, probiotics also regulate immune response through their interaction with immune cells in gut-associated lymphoid tissue (GALT), enhance immune tolerance, and suppress chronic inflammation (Ballini et al., 2023).

Prebiotics (as opposed to probiotics, which are live organisms) are selectively fermentable fibers—fructooligosaccharides (FOS), inulin, and galacto-oligosaccharides (GOS)—as well as other non-bacterial food molecules that preferentially expand the growth of beneficial bacterial species, including Bifidobacterium and Lactobacillus. Prebiotics indirectly promote gut health, immune function, and metabolic health by encouraging the growth of healthy bacteria (Wu et al., 2017). Prebiotics also stimulate SCFA production, which facilitates acidic gut environment that limits pathogenic growth. In addition, such SCFAs help with mineral absorption, blood sugar control, and maintaining healthy levels of cholesterol. According to a research, prebiotics help bolster digest biological defence and cognition via modulation of gut microbiota composition (Peng & Biswas, 2017).

Combination of probiotics and prebiotics creates “synbiotics,” which are specific type of formulations that provide a survival advantage to beneficial bacteria when they enter the gut. Synbiotics are increasingly studied to promote favorable gut microbiome as well as metabolic and immune health. The literature shows how synbiotics improve probiotic efficacy by providing resources that support the growth of probiotics. The synergistic relationship between synbiotics and probiotic is fundamental for a healthy microbiome, and as such both in combination are integral for the overall health (Khan et al., 2020).

3.5. Fortified and functional beverages

The nutraceutical food sector is spotting growth in the fortified and functional beverage category, targeting a shift from basic hydration to health benefits. These drinks are fortified with nutrients, bioactive compounds, and functional ingredients to promote targeted health results, including immune support, cognitive enhancement, gut health, and energy metabolism (Puri et al., 2022). Owing to the development of food technology and consumer interest in health and wellness, these drinks are convenient products to make consumers healthier.

Fortified beverages are the drinks having additional vitamins, minerals, and other nutrients that may not be supplied in good quantity through diet. Some examples are immediate juices fortified with calcium or vitamin C, plant-based milk with vitamins D and B12, and electrolyte drinks with potassium and magnesium (Gupta et al., 2023). These fortified drinks help to fulfil nutrient deficiencies in the deficient population, such as vitamin D-fortified milk for people having low sun exposure, or iron-enriched juices to prevent anemia in high-risk populations.

Micronutrient-fortified beverages are designed to match the dietary needs of different population groups, such as children (i.e., healthy growth), athletes (i.e., recovery), and elderly individuals (i.e., nutritional boost), allowing them to receive micronutrients lacking in normal diet, without requiring substantial changes in food intake composition. They are infused with bioactive ingredients, such as antioxidants, probiotics, prebiotics, adaptogens, herbal extracts, and Omega-3 fatty acids, thus targeting the areas, such as immunity, mental alertness, and gut health. Some popular functional beverages are probiotic-packed kombucha, green tea with infused antioxidants, and turmeric lattes with anti-inflammatory properties (Ward, 2017). Fortified beverages emphasize on preventing deficiency whereas functional beverages are mostly concerned with encouraging well-being and helping the body’s natural functions (Dini, 2019).

4.1. Barley

Barley (Hordeum vulgare), one of the world’s oldest cultivated grains, is increasingly recognized as a nutraceutical food because of its diverse range of phytochemicals and bioactive compounds, which provide health benefits beyond basic nutrition. With its impressive nutritional profile and an array of health-promoting properties, barley is a rich source of dietary fiber, vitamins, minerals, and a variety of phytochemicals, making it a valuable addition to nutraceuticals and functional foods.

Barley is one of the cereal grains that contains a lot of soluble and insoluble dietary fibers and other bioactive ingredients, including tocotrienols (form of vitamin E), vitamin B-complex, minerals, and phenolic compounds. Important phytochemicals found in barley and their health benefits are explained in Table 2. Antioxidant activity of phenolic compounds is widely studied and is thought as partly, if not entirely, due to their phenolic hydroxyl groups, including the classes such as phenolic acids, tannins, flavonoids, pro-anthocyanidins, and amino phenolic compounds. Consumption of whole grain barley and its hydroalcoholic extracts reduces the onset of chronic diseases because of phytochemicals such as β-glucan, phenolic acids, flavonoids, lignans, phytosterol, and folate.

4.2. Flax Seed

Flaxseed or linseed (Linum usitatissimum), in India also known as alsi, jawas, or aksebija, belonging to the family Linaceae. It has a glossy and smooth appearance seed coat, which is hard in nature with desirable flavor, and a range of color from dark brown to yellow. It looks like a tiny nut (3–5 mm), which is slightly more pointed at the top than at the base. Since pre-historic period, flaxseed cultivation is widely prevalent in India, Europe, and Egypt. Presently, flaxseeds are used as a food and are also known for their medicinal properties. Although flaxseed is an underutilized oilseed, it has gained popularity over the past few decades because of its favorable nutritional profile and other functional properties.

Flaxseeds through times have evolved as one of the leading ingredients of functional food products because of nutritive and functional properties (Ganorkar & Jain, 2013). Flaxseed is a good source of omega-3 fatty acid among non-fish consumers. Owing to its high nutritional value, it is a potent functional beauty ingredient. As a functional food, it has become an emerging powerhouse of global food supply. Numerous studies have shown that the consumption of flaxseed aids in the lowering of high blood pressure and cholesterol levels, the two major reasons for cardiovascular diseases.

Being a good source of alpha-linolenic acid, lignans, proteins, phenolics, flaxseed is one of the most promising functional foods (Table 3). It has acquired herbal history since antiquity because of its therapeutic properties against many diseases, such as diabetes mellitus, arthritis, osteoporosis, cardiovascular diseases, and cancer. Compared to other plants, flaxseeds contain a high amount of lignans (600 mg kg^–1).

4.3. Rice Bran Oil (RBO)

Rice is a staple for a large portion of Asia’s population. Rice bran is the brown layer of rice obtained after removing the outer husk during paddy milling. Rice bran oil is among the richest sources of bioactive phytochemicals and has great commercial significance. Although not new, RBO is a less popular cooking medium used in Asian countries, such as India, Japan, and China.

With a paddy production of 150 million tons, RBO is one of the promising functional edible oils in India. This policosanol is extracted from RBO, which can be isolated by various extraction methods, including solvent or n-hexane-based extraction, Ohmic heating, and supercritical fluid extraction. Known as “heart oil,” RBO is extremely popular in Japan for being a preferred cooking medium. RBO is a known functional food or health food in Western countries (Nayik et al. 2015).

As per the standards of “Codex Alimentarius,” RBO must have a relative density of 0.910–0.929, refractive index of 1.467–1.470, and an iodine value of 136–148. RBO is extracted from the germ and inner husk of rice and mainly consists of gamma-oryzanol, vitamin E complex, tocotrienols, and β-sitosterol (Chotimakorn et al., 2008). The major unsaturated fatty acids in RBO are oleic acid (38.4%), linoleic acid (34.4%), and α-linolenic acid (2.2%), and the main saturated fatty acids are palmitate 54 (cetyl palmitate; 21.5%) and stearate 52 (double-pressed stearic acid with a specific composition; 2.9%). In crude RBO, content of gamma oryzanol ranges from 1.5% to 2.9% (w/w) (Paucar-Menacho et al., 2007). The crude or unrefined RBO is subjected to physical (Arumughan et al., 2003) or chemical refining (Gopala Krishna et al., 2006) to meet the standards of other edible vegetable oils.

5.1. Definition and Process

Extrusion technology is a well-established and widely used process for the preparation of food products. It impels food constituents through a combination of mechanical and thermal treatments to obtain desirable textures, shapes, and functionalities (Prabha et al., 2021).

Extrusion process drives food ingredients through a cylindrical barrel containing one or two rotating screws. The material is heated, pressured, and exposed to mechanical shear as it flows through barrel (Bordoloi & Ganguly, 2014). Following steps are involved in the Extrusion process:

Temperature: For all food products and texture requirements, extrusion barrel’s temperature is maintained at 90–200°C. These high temperatures maintained for extended periods gelatinize starches and denature proteins while also inactivating many pathogens and spoilage organisms that may affect product safety and desired textural characteristics (Yacu, 2020). Temperature must be controlled very precisely, as it influences the texture and nutritional quality of the finished product (Alam et al., 2016).

Pressure: As screw rotates, the die at the exit of the extrusion barrel builds up high pressure inside. With a high pressure of up to 100–150 bar, it is easy to curl and squeeze in the ingredients (Shelar & Gaikwad, 2019). Using a combination of heat and pressure, the moisture content is decreased, thus resulting in a dry and expanded product discharged from the die (Bouvier & Campanella, 2014).

Mechanical shearing: The mechanical shearing force applied to food material by rotating screw(s) helps in mixing, kneading, and/or extrusion of the material. This mechanical shearing destroys the structure of food matrix, resulting in homogeneous mixing of ingredients and changes in texture (Sule et al., 2024). The shearing force influences protein alignment and starch gelatinization, thereby providing specific structure functionality and texture to extruded foods (Arêas, 1992).

When the pressurized food material exits barrel through inside die, it decompresses and then rapidly expands and cools to produce end products that are porous and crispy (e.g., snack foods). The effect depends on the formulation, water content, and preparation conditions (Schmid et al., 2022).

5.2. Advantages of Extrusion Technology for Nutraceuticals

The key features of extrusion technology are its versatile and efficient processing, stability, and long shelf life, thus making it very favorable for the food sector.

5.3. Nutrient Retention and Bioavailability

Extrusion technology while producing nutraceuticals is able to keep the stability and bioavailability of key nutrients. The process of extrusion minimizes nutrient loss because of favorable conditions of high temperature and pressure (Camire et al., 1990). Although some vitamins and sensitive bioactive constituents might be prone to heat, extremely short extrusion time (generally from seconds to minutes) minimizes the exposure and helps to maintain the relative potency of antioxidants and other micronutrients, such as minerals and vitamins (Gulati et al., 2020). This is important for bioavailability of nutraceuticals with health benefits, such as immune support and cardiovascular health (Choton et al., 2020).