Industrial applications of kale (Brassica oleracea var. sabellica) as a functional ingredient: a review

ABSTRACT This review highlights the adaptability and impact of kale (Brassica oleracea var. sabellica) in the food industry. An overview has been provided of the valuable natural source of various bioactive compounds including proteins, pigments, polyphenols, chlorophyll, vitamins, and minerals. Numerous biological effects, such as antioxidant, antibacterial, anti-cancer, anti-inflammatory, and anti-diabetic properties, are displayed by these bioactive substances. Due to taste preferences and convenience, this vegetable is typically processed at home or by the catering and foodservice companies. The seasonal, perishable vegetable’s shelf life can be prolonged by using preservation techniques (freezing and canning) with blanching. The physical and chemical characteristics of kale are altered by cooking, blanching, freezing, and canning. Numerous studies on the effects of different treatments and storage conditions on various kale quality metrics have been published. As a result, the waste generated during kale processing has the potential to provide economic benefits by reentering the food processing line as a food additive while providing sustainable and innovative solutions for food waste recovery.


Introduction
Kale is a leafy vegetable with numerous varieties. However, different varieties of kale are distinguished by their leaves (glossy bluish/green), shapes (flat/thick), and abundance of tiny flower curds (similar to those seen in broccoli). [1] The nutrient-dense vegetable kale (Brassica oleracea var. sabellica) is a semiannual or perennial vegetable. The kale plant is separated into three parts including roots, leaves, and stem. The leaves and stem are utilized for medicinal and nutraceutical purposes. Brassica olerace var. acephala can be smooth curly and quite attractive leaves. This leafy vegetable is quickly becoming popular all over the world due to its nutritious makeup. These are eaten in both raw and processed forms. [2] These curled, beautiful leaves are particularly challenging to eat when they are fresh. The Latin word for "kale" is Brassica oleracea, sometimes known as borecole, and it is a member of the Cabbage family. Due to his extensive nutritional composition, the Nigerian was given the moniker "hospital too far." This crop is produced yearly, it is harvested in two months, and depends on the variety and growing conditions. [3] In addition to antioxidants like tocopherol, beta-carotene, ascorbic acid, Kale has been found high in macro minerals and micro minerals, fiber, phytochemicals (polyphenols, lutein, and zeaxanthin), both lipid-soluble and water-soluble vitamins and bioactive compounds. These valuable compounds are preserved by using different processing technique. Due to rich sources of nutrients and bioactive compounds, kale vegetable played important role against various chronic diseases. [4] The aim of study showed that different processing technologies are played valuable role in the preservation of nutrients and bioactive compounds on industrial level. The industry is adopted combination drying technologies as a result of rising concerns over product quality and manufacturing costs. [5] Commercial applications of kale In recent decade, peoples are become more interested in intake of antioxidant enrich vegetables. In vegetables, kale (Brassica oleracea var. sabellica) have been recognized as good source of antioxidant as compared to other vegetable sources. Kale contain high amount of phytochemical compounds (active chemicals) in their plant tissues. Therefore, kale (Brassica oleracea var. sabellica) have ability to reduce risk of chronic diseases such as, diabetes, arthritis, cancer, and cardiovascular disorders. [6] In the global superfood market, demand for organic kale powder is rapidly increasing to prepare of functional products for multiple purpose, notably pharmaceutical, nutraceutical, beverage and food industries. The food and beverage industry employs organic kale powder to boost the nutritional content of a variety of prepared foods and beverages, including smoothies and juices. In addition to the food industry, it is anticipated that the demand for organic kale powder in the superfood sector would remain high due to good functional properties. Leading manufacturers incorporate organic kale powder into their nutraceutical and nutritional supplement products because of its range of health advantages. Organic kale additionally includes a number of trace elements, such as Ca 2+ , K + , Mg 2+ , Fe 2 + , Na 2+ , Zn 2+ . These are recognized for their antibacterial and anticarcinogenic qualities. Moreover, plant lipids have become increasingly popular as functional components in the creation of functional foods among all bioactive phytochemicals. These include galactolipids, polyunsaturated fatty acids, oleic acid, phytosterols, fatty alcohols, carotenoids, diglycerides, and medium-chain triglycerides. The term "functional ingredients" is used to describe bioactive substances that have been demonstrated the beneficial effects including improving human health as well as lower the risk of pathological diseases. [7,8] Despite the fact that frying kale chips drastically decreases their nutritious and phytochemical content, they have become very popular in the food sector. [9] Kale seeds can also be used as a source of raw oil in breads and pastries as addition to the leaves. Biegaska-Marecik et al., [10] reported that development of innovative functional meals utilizing apple juice-based drinks with the addition of freeze-dried kale leaves that are a good source of vitamins, minerals, and healthy phytochemicals. Although other Brassica plants (white cabbage) are commonly fermented vegetables. Kale has been historically prepared and consumed in this manner (sauerkraut). Kale juice was produced by using Lactobacillus strains that had great nutritional properties. In addition to being cooked in a variety of soups, omelets', and stir-fries, kale juice and salads made with raw kale leaves are the most popular ways to consume kale. In Europe, smoked pork is frequently eaten with kale. Hence, on rare occasions, pickles are made using certain plant parts. [11] It may be challenging to determine that kale or cabbage was used in traditional medicine (acephala group) because all green Brassica crops have the same name. Since other Brassica crops have long been used to cure problems like gastritis and stomach ulcers. kale's use in traditional medicine is pretty analogous to that of those other Brassica crops. [12] Moreover, B. oleracea var. acephala had been used to treat bone disorders, diabetes mellitus, vision problems, liver diseases and obesity. [13] Table 1 Processing and preservation of kale The Cruciferae family vegetable kale (Brassica oleracea var. sabellica) are consisting of vitamins K, C, E, and as well as glucosinolates, carotenoids (zeaxanthin, carotene and lutein), and several bioactive compounds with anti-inflammatory antioxidant activities. Cutting, blanching, and heating of raw material before preservation have positive effects on tissue loosening and protein digestibility, but they also induce the leaching of mineral compounds. [24] The most popular method utilized while preparing these veggies for food preparation is cooking. Food processing methods that have the least impact on their chemical composition. These are being discovered and established through food technology. To maintain the beneficial and bioactive elements of vegetables, it is crucial to know how to optimize processes such standard cooking. [25] Table 2 Freezing method Kale leaves are processed in the following steps before being frozen: washed, sliced into strips (approximately 3 cm widen), fried or blanched, cooled, dripped on sieves. In classical approach (variant Winterbor kale is typically cooked due to its thicker leaves, but it can also be eaten raw. It is a popular type of curly kale that is favored by both commercial growers and home gardeners due to its high antioxidant activity. It is one of the cold-hardiest kales, meaning it can withstand freezing temperatures. [13,14] Lacinato Kale Dark green and blade-shaped leaves Height (3 feet) Lacinato is tender, making it ideal for use in salads. It's also delicious in soups, frittatas, and other cooked dishes.
Lacinato is high in minerals that most Americans do not consume, such as and zinc. It's also contain fiber, vitamins C and K. [13,15] Scarlet Kale Purple leaves and stalks Young, tender leaves can be eaten raw in salads, while mature leaves can be cooked and added to soups or grain dishes.
Scarlet kale had the highest amount of total tocopherols and alpha tocopherols in a study that compared eight kale cultivars. [13,16] Red Russian Kale Baby leaf kale is especially tasty raw in salads.
Its contain minerals (manganese, copper, calcium, and magnesium) and vitamins (A, K, C, and B6). [13,17] RedBor Kale Deep reddishpurple leaves Height (2-3 feet) Its leaves are crisp when raw but tender when cooked, making it an excellent addition to stews and pastas. Its leaves can also be finely shredded to make a bright and crisp raw salad.
Redbor kale contains a lot of nutrients (vitamins A and C, as well as Fe 2+ , Ca 2+ , Mg 2+ , K + , protein, polysaccharides, and dietary fiber). [13,18] Beira Kale Thick stems Green Height (2 feet) Beira has green leaves that are used in a traditional dish called Portuguese kale soup.
It is rich source of antioxidants (glucosinolates). [13,19] Darkibor Kale Thick stems Height (2 feet) It is used in raw and cooked form It is good source of antioxidants [13,20] Walking Stick Kale Walking stick kale Massive leafy green.
Because of their tender texture, most people prefer to eat the younger leaves. The tougher, older leaves make excellent animal feed.
It is rich source of nutrients and antioxidants. [13,21] Japanese Flowering Kale

Rosette Fuschia center and green outer leaves
The frilly leaves add to the overall visual appeal. It also makes great kale chips.
The iron-rich flat leaves are easy to chop and high in vitamins A, C, and E. It is also a natural breath sweetener due to its high chlorophyll content. [13,22] Thousandhead Kale

Height 6 feet Massive leaves
The leaves are only slightly curled at the tips, making pests like caterpillars easier to spot.
Its contain carotene which can help prevent in different diseases. [13,23]  Carotenoids contents had been found to be decreased.
HPP had been found to be effective for kale lipophilic nutrients [27] Kale raw leaves and blanched Blanching, cooking, freezing, canning or drying Temperature.
time, freezing and humidity The average levels of chlorophylls and carotenoids in freeze-dried products were higher.
Minimal changes occurred in chlorophylls and carotenoids values of kale [28] Fresh kale leaves Blanching and cooking Position of sieves, time and temperature The preliminary use of blanching as a treatment improved GLS retention in dried leaves due to the inactivation of myrosinase.
The minimal GLS losses were in frozen kale leaves whereas the highest loss was in sterilized and dried. [29] Fresh and frozen kale leaves Blanching or cooking Temperature and time Frozen products from blanched raw material contained the highest amounts of antioxidants, total polyphenols and vitamin C Frozen products retains the highest phenolic contents [26] Fresh and processed Blanching Temperature and time Both fresh and processed leaves of kale were a good source of amino acids In kale leaves, both fresh and processed, minimum changes were observed in amino acid contents. [30] I) had been formed by blanched kale leaves to produce a final frozen product, while (variant II) had been produced a product from kale leaves that have been cooked to a consistency. In version I, kale was blanched for about 2.5 minutes at 96 to 98°C in a stainless-steel tank with a 5:1 (weight-to-water ratio). Blanched material was dripped over sieves for 30 minutes after being chilled with cold water. In version II, kale was boiled in water for 10 minutes in a stainless-steel container with a 5:1 (weight-to-water ratio). [29] After cooking, a stream of cold air was used to chill the sieve residue. The materials from the blanched and cooked samples were wrapped in 500-gram polyethylene bags and frozen at 40°C. Frozen goods was kept in a chamber freezer between 20 and 30°C until further analysis. [29] Sterilization method After freezing, kale leaves were blanching, washing, grinding /cutting into strips (2-3 cm broad), adding hot water, filling metal cans (0.8 L in volume), preserving (sterilization), canning and sealing. From the raw materials that were cut and ground, two types of products were produced. Kale that has been ground up, it can be served as a side dish or utilized as a vegetable element. The same procedures as for freezing were used for blanching. The leaves were ground in an 8 mm mesh electric mill. The following thermal processing stages were utilized to sterilize in a pressure sterilizer including heating at 100°C (10 minutes), heating up to 118°C (15 minutes), sterilization up to 118-120°C (80 minutes), cooling at 100°C (15 minutes), and cooling at 30°C (10 minutes). Cans of processed kale were allowed to fully cool and dry before being kept there until analysis. The temperature of the room was kept below 10°C. [29] Drying method Food drying is a complex process that involves mass and energy transport in a system at the same time.
The removal of moisture from food is typically accompanied by a phase change such as, evaporation or sublimation. In this process, thermal energy is supplied to facilitate phase change and moisture removal. It is one of the most energy-intensive processes in the food processing industries due to the interactions of water molecules with biopolymeric matrices, as well as an increased enthalpy of evaporation when the moisture content of the product is low. [31] Various drying techniques have been developed and tested over the years to improve dried product quality retention and drying efficiency. Among various drying technologies, hot air drying, spray drying, freeze drying, and any new drying method that can deliver significantly improved quality have frequently been investigated for the purpose of selecting the right drying method for a target product in terms of product quality, production costs, and, more recently, process sustainability and low carbon footprint. [32,33] Kale leaves that had been blanched and unblanched were both dried using hot air or freeze-drying to the required humidity level (below 5%). The following preparation procedures came before the drying process: For blanched samples, remove the main vein, rinsed, sliced into 2 cm long pieces, and blanched for about 2.5 minutes in 96 to 98°C water with a leaf-to-water (weight ratio of 1:5), cooled, and let the liquid drained over sieves. [34] Traditional and new drying methods are available in the market for multiple purposes. Several studies have attempted to compare different drying technologies using product quality as a criterion.

Hot air-drying (AD)
Hot air-drying (AD) process has been used to drying fruit, vegetables, and mushrooms, this process is carried out using a specially designed equipment. In this process, hot air was blown on cut kale leaves at temperature 50°C in first sieve. To avoid crusting and roasting of the drying phase at the end, sieve positions were switched every 30 minutes. It took 5.5 hours of drying time to get the humidity down to the intended 5% level. After drying, various batches of dried kale material were combined and put into airtight jars (2.0 L glass twist-off jars in volume). [25]

Freeze-drying (FD)
In freeze-drying (FD) process, main part was removed, washed, cut (about 2 cm long). After that, blanched for about 2 minutes in water at 98°C, then cooled and dipped on sieves. The freeze-drying process began at a specific temperature of 25°C in a specific lyophilizing cabinet. This process automatically stops, when the temperature of the dried material, in the lyophilizing chamber reached about 30°C after 30 hours of drying. After drying, the trays' contents were combined and stored in airtight containers (glass twist-off jars 2.0 L in volume). Until further investigation, this dried samples were stored at two different temperatures: Cold temperature (C) (8-10°C) and ambient temperature (A) about (18-20°C). [29] Nutritional composition of kale In the recent decade, researchers and scientists have become more interested in nutritious foods, one of these foods being kale. Kale (Brassica oleracea var. sabellica) is a leafy, green cruciferous vegetable that is high in nutrients and minerals. It can provide a variety of physicochemical benefits to the human body after consumption. Kale typically contain 3.6% dietary fiber and 8% total carbohydrates. Kale is the best source of triglyceride, folate, nicotinic acid, and vitamins C, K +2 , A, B 6 , B 2 , and B 1 when compared to other cruciferous vegetables. It is also said to be high in macro-as well as micronutrients such as sodium, K + , Mg 2+ , Ca 2+ and Fe 2+ . Kale contains more than 1,000 times the daily recommended amount of vitamin K, 98 times the amount of vitamin A, and 71 times the amount of vitamin C. Therefore, kale has recently attracted the interest of nutraceutical industry because of its good human health properties. [35,36] Kale also contain small amounts of oxalates, which are minerals that include Ca, Na, K, Fe, Mg and Cu, according to preliminary studies. The mineral requirements for Ca 2+ , Mg 2+ , K + , Mn 2+ and Na 2+ can be satisfied by a portion of 250 ml of green curly kale juice 63%, 38%, 22%, 18%, and 89%, respectively. [37] In addition, one cup of raw kale contains 33 calories and 7 grams of carbohydrates which is good for the health of gut microbes. It is a very healthy vegetable for diabetics and those trying to lose weight. [38] According to the 2015 Dietary Guidelines Advisory Committee, a 100-gram serving of fresh kale can provide 188 to 873 milligrams of K+, 35 to 300 milligrams of Ca2+, and 20 to 100 milligrams of Mg2+ recommended daily intake for peoples. The prebiotic carbohydrates in this portion of kale range from 0.4 to 6.7 g and include 45.4 to 59.8 mg (sugar alcohols), 0.4 to 3348 mg (carbohydrates), and 245 to 703 mg (hemicellulose). [39] Fresh kale also contains 36-98 calories and 1.6-5.9 g of total per 100 grams, which are both low amounts. The two main soluble sugars found in kale are glucose and fructose. Prebiotics, micronutrients, and calories are all abundant in kale. It contains naturally occurring dietary fibers and sugar alcohols that are good examples of prebiotic. In prebiotic, monosaccharides, disaccharides, polysaccharides and fructooligosaccharides are considered as a rational approach to alleviating various chronic diseases such as, metabolic disorders, cardiovascular, inflammation and cancer. [40,41] Nonstarch polysaccharides, resistant starch (RS) and other non-digestible starch polysaccharides make up dietary fiber. Simple sugars are the source of sugar alcohols like that sorbitol and mannitol, among others. In kale, there were a total of 0.4 to 6.7 gram of recognized prebiotic carbohydrates per 100 g, but there were also 5.0-8.0 g of unknown soluble carbohydrates. [31] In a recent study, the CFDC (Centers for Disease Control) ranked bananas 47th among vegetables and fruits that were significantly associated with a lower risk of other non-communicable diseases and cardiovascular disease. Moreover, based on nutritional contents listed in the USDA (National Nutrient Database), kale is ranked 15th due to its excellent nutraceutical and medicinal properties. [35] Nutritional composition of kale as shown in Figure 1.

Anti-nutritional/bioactive compounds in kale
Kale has been recognized as an excellent source of carotenoids, glucosinolates, polyphenols, and vitamins C and E. Kale's high sulforaphane content stimulates the gene called Nrf2 (nuclear factor erythroid 2-related factor 2), which enhances sensitivity to insulin as well as provides protection against by the oxidative damage triggered by hyperglycemia such as, nephropathy, retinopathy, and cardiomyopathy. Kale contain more total polyphenols than any other cruciferous vegetable, phenolics, tannins, flavonols, anthocyanidins, flavones and coumarins, one of the phenolic compounds found in green vegetables. [37,42] Nitrate is a typical component of plants that is discovered as a result of microbial attack. Plants use nitrate from the soil as nitrogen for protein synthesis. Protein production in plants depends on photosynthesis, however as light levels decrease, photosynthesis declines, causing nitrate to accumulate in cell fluids. [43] According to reports, vegetables cultivated in dim light have higher nitrate concentrations than those produced in bright light. In general, genetics and growth conditions dictate a plant's nitrate concentration. [44] According to Erdogan and Onar [45] Nigerian kale has a phytate concentration of 0.12 mg per 100 g and a tannin concentration of 0.15 mg per 100 g. Phytate concentrations in the following leafy vegetables range from 0.58 to 0.811 mg per 100 g, according to Agbaire [46] Cassava leaf (Moni esculenta), Bitter leaf (Vernomia anydalira), Water leaf (Talinum triangulare), Ugu leaf (Teiferia occidentalis) and Green vegetable (Amaranthus spinosus). The phytate concentration in kale examined Agbaire [47] has found to be low as compared to GLVs about (0.412 to 1.3 mg per 100 g), The tannin content has found to be lower than the phytate level in different GLVs about (0.004-0.026 mg per 100 g). Phytate has antinutritional effects on human body function and contributes to iron and zinc deficiency by strongly chelating Ca 2+ , Fe 2+ , and Zn 2+ to form an insoluble compound. [48] Phytate, on the other hand, has a nutritional role in cancer prevention and acts as an antioxidant. [49] According to reports, accounts for sixty to eighty percent of the PO 4 in legumes, cereals, oilseeds, and nuts. Phytate levels are lowest in tubers, roots, berries and fruits. [50] Antinutritional/bioactive compounds in kale as shown in Figure 2.

Therapeutic potential of kale
Kale is leafy vegetable that belongs to cabbage family, and contains different nutrient and bioactive compounds. These compounds are played an important role in human health. Table 3 Antimicrobial spectrum of kale Fruit and vegetable juices are among the nondairy fermented foods that are becoming more and more popular with customers globally for both monetary and health-related reasons. Curly kale juice's spontaneous fermentation produced phenolic, ascorbic acid, mineral and cd (cadmium) content as well as antimicrobial and antioxidant activities. It inhibits the growth of E. coli or Salmonella spp. Hence, the fermentation process significantly increases the growth of lactic acid bacteria, enterococci, and yeasts. [37]

Kale anti-carcinogenic characteristics
Sulforaphane, a special cancer-fighting chemical, is abundant in kale. Sulforaphane promotes detoxification by provoking phase II detox enzymes as well as enhancing antioxidant enzymes. [58] Sulforaphane inhibits a group of enzymes that has been found in alteration of expression of genes and produce cancer-causing protein molecules. Importantly, researchers found that kale boosts the body's production of immunoglobulins (Ig), that the immune cells uses to recognize and completely eradicate foreign invaders. [59] Researchers in Italy found that people who ate green leafy vegetables like kale at least once per week had a 17% lower risk of developing oral, colorectal, and breast cancers, as well as a 28 and 32% lower risk of developing esophageal and kidney cancers. However, due to a particularly abundant amount of glucosinolates, which the body converts into cancer-preventive substances called isothiocyanates, in terms of cancer prevention, kale could even surpass other cruciferous vegetables. [60] These complex substances are powerful inducers of cancer-destructive enzymes as well as carcinogenesis inhibitors. As a result of several different chemicals, it has been observed to significantly reduce the risk of various including cancers, breast, pancreas, colon, and esophageal cancer. Furthermore, it has been demonstrated that the water-soluble portion of kale increases human cell immunoglobulin production. Sulforaphane has clearly been shown to specifically target pre-cancerous cells, acute and chronic disorders. [61] Kale ability to fight against free radicals According to recent research work, the carotenoids in dark green leafy vegetables like kale can work as antioxidants and strengthen the body's natural defenses against free radicals. These safeguards aid in preventing free radicals from damaging DNA, which can result in cancer. Kale contains vitamin C, a potent antioxidant that works to prevent the synthesis of carcinogens. Similar to other leafy greens, kale has a high antioxidant content. It also contains flavonoids and polyphenols, as well as beta-carotene and vitamin C. Antioxidants are chemicals that aid in preventing the body's oxidative damage caused by free radicals. [62] Oxidative damage is thought to be one of the main causes of aging and a number of illnesses, including Leaves and stems contain macronutrient and phytochemical that play an essential role in the prevention of different diseases [51] Kale Phenolics, carotenoids, and glucosinolates

Chronic and degenerative diseases
This review discussed the effects of abiotically stressed kale on the prevention and treatment of chronic and degenerative diseases. [52] Kale Prebiotic carbohydrates, unsaturated fatty acids and different vitamins Coronary artery disease, inflammatory, genotoxic and gastrointestinal diseases kale plays a protective role in rent diseases [53] Curly kale juice Phenolic, vitamin C and minerals Antimicrobial and antioxidant activity The study indicated that fermented curly kale juice may become popular in the functional food sector [54] Kale juice Protein, carbohydrate, vitamins and minerals Coronary heart disease The study suggested that kale juice reduces the risks of coronary artery disease in male [55] Kale and papaya

Prebiotic Inflammation
The study suggested that both vegetables showed prebiotic and anti-inflammatory effects in the TNBS model of rat colitis [56] Kale extract Raw kale plant kaempferol-glucosides The outcomes suggest that Lactobacillus paracasei A221 is effective in enhancing the anti-aging properties of kaempferolglucosides [57] cancer. However, many chemicals that are antioxidants serve for other crucial purposes. Among these chemicals, the flavonoids quercetin and kaempferol are very important, which are found in abundance in kale. They have powerful anti-inflammatory, antiviral, anti-depressant, blood pressure-lowering, heartprotective, and anti-cancer properties. [63] Kale impact in the prevention of diabetes For diabetics, fiber-rich foods such as kale (Brassica oleracea var. sabellica) have beneficial effects on health, including hypoglycemic impacts, which can also help prevent postprandial blood sugar spikes. In a previous clinical research work, intake of kale-containing food at a dose of 14 g reduced the postprandial plasma glucose levels in the patients. [64] In another research work found that the eating green vegetables more those peoples have not diabetics diseases due they can help regulate blood sugar levels and lower the risk of type 2 diabetes. [65] Conclusion This review provides up-to-date information on the potential industrial food applications of kale (Brassica oleracea var. sabellica). Waste generated in the kale processing industry has been identified as a potential source of bioactive compounds as well as other valuable compounds with high potential for industrial applications such as functional food ingredients, food colorants, and others. Furthermore, the industry is shifting toward more environmentally friendly methods of extracting bioactive and other compounds from kale, while prioritizing more sustainable solutions for utilizing waste generated in the kale processing industry. The review also focused the critical importance of considering the safety aspects of compounds recovered from kale because transforming waste into food additives introduces a novel loop into the food supply chain that has not been thoroughly investigated in terms of food safety. Studies on industrial scale applications are limited. To find constraints and promise for large-scale applications, it is necessary to translate laboratory-size studies to an industrial scale. By turning trash into food additives, the productive partnership between academic and industrial parties may open up chances to increase the value of kale processing chains.

Disclosure statement
No potential conflict of interest was reported by the authors.