The guava fruits are characterized by high water content (84.9%) and low content of carbohydrates (13.2%), fats (0.53%), and proteins (0.88%) (Medina and Pagano 2003). Proximate composition is given in Table 1 (Conway, 2002; Iwu, 1993; Fujita et al. 1985; Hernandez, 1971; Conway, 2002). Beside this many other important compounds such as hexanal (65.9%), γ-butyrolactone (7.6%), (E)-2hexenal (7.4%), (E, E)-2,4-hexadienal (2.2%), (Z)3-hexenal (2%), (Z)- 2-hexenal (1%), (Z)-3-hexenyl acetate (1.3%) and phenol (1.6%) were reported from fresh guava fruit extract. Certain essential oils extracted from guava are 3-caryophyllene (24.1%), nerolidol (17.3%), 3-phenylpropyl acetate (5.3%) and caryophyllene oxide (5.1%) (Paniandy et al. 2000), and few active aromatic constituents from pink guava fruit such as 3-penten-2-ol and 2-butenyl acetate were isolated (Jordan et al. 2003). Ascorbic acid is the main constituent of guava as antioxidant (Charles et al. 2006). The genus citrus is well known for its pharmaceutical importance. The peel extracts of Dargiling Orange (C8), South African Malta (C5), Kagja Lemon (C2), Batabi Lemon (C4), Elachi Lemon (C3), Kagja Lemon (C2) and Kagji Lemon (C1) show excellent antimicrobial potential against various bacterial strains e.g., B. cereus, S. aureus etc. (Afroja et al. 2017). The strong odour of the fruit is attributed to its carbonyl compounds (Dweck, 2001). There is a growing trend to use the medicinal plants as the natural resources in order to develop new drugs. The natural products are applied to treat various viral, fungal and bacterial diseases. The antimicrobial activities of alcohol fruit extracts from guava (Psidium guajava) were compared to those of pineapple (Ananas comosus) and apple (Malus pumila). Eight bacterial strains including Pseudomonas aeruginosa, Klebsiella, Enterococcus faecalis, Shigella flexineri, Enterobacter cloacae, Enterotoxigenic E.coli (ETEC), Enteroaggregative E. coli (EAEC) and Staphylococcus aureus were used for antimicrobial evaluations. The fresh fruits of the above mentioned plants were purchased from the market; then they were cut into small cubes and finally dried over 4–5 days in sun to a crisp. The pieces were blended to the fine powder; finally methanol extracts were obtained by passing 75 g of each powder through a Soxhlet apparatus having 250 ml of 99% methanol. The same process was performed with 250 ml of ethanol to produce a methanolic crude extract. The sample extracts were evaluated using agar well diffusion method. Norfloxacin and water were used as positive and as negative controls, respectively. The extracts caused the inhibition of microbes; the zones of inhibition were measured and an activity index was calculated from the mean zone sizes. It was concluded that all the fruits possess some antimicrobial potential; the highest activity index (2.6) was observed from pineapple extracts against EAEC. The pineapple fruit displayed strong potential against all the bacteria. The guava extracts possessed the antimicrobial potential against all the microbes with the exception of ETEC. The methanolic and ethanolic extracts of apple were found active only against EAEC and Staph. Aureus. The methanolic extracts of guava and apple were found active as compared to the ethanolic extracts while the ethanolic extracts of pineapple showed slightly larger inhibition zones. The results of this investigation show great promise for potential antimicrobial drugs (Samiha Kabir et al. 2017). Table 1 details the phyto constituents on different parts of guava.

Guava (Psidium gujava) has a long history to be used in treatment of different ailments e.g. anti-inflammatory, diabetes, hypertension, caries, wounds, pain relief and reducing fever in traditional and folk medicines (reference would be appreciable). However, the therapeutic significance of guava for disease curing has gain attention over last decade. The guava fruits are observed to have fungicidal action against Arthrinium sacchari M001 and antimicrobial activity against Chaetomium funicola M002 strains (Sato et al. 2000). Similarly, the ethanolic extract from the shell of ripe fruit presenting activity on Streptococcus mutans and Escherichia coli (Neira and Ramirez, 2005). Guava was also found resistance against malarial infection. An in vitro study of antiplasmodial assay carried out on malarial parasite, Plasmodium falciparum strain D10 showed antigiardiasic activity with trophozoite mortality (87%±1.0), intending the anti malarial effect (Nundkumar & Ojewole, 2002). The important therapeutic properties of guava against metabolic disorder, diabetes, obesity and antioxidant are discussed.

Guava fruit is frequently used in various indigenous medicinal practices in different countries. The preparations of guava extract traditionally are in the form of infusion, decoctions, and tinctures in order to increase the level of guava as dietary supplement. To combat the scarcity researches have focused in the development of different formulations by preserving the nutraceutical properties of guava for fortification like milkshakes, curd and other low fat calorie products (Menezes et al. 2012). The popular products of guava as jellies and preserves are saturated in the market. However retaining the functional characteristics is an important factor while preparing new formulations (Gonzalez et al. 2011; Rajoria et al. 2013). In the development of a new product, with addition of concentrated fruit juice, the determination of its rheological parameters is an essential aspect, as the use of pre-existing parameters in industry could easily include some process errors while designing the processes such as pumping, stirring and transport in pipelines (Branco et al. 2005).

The most efficient method of production of guava fruit powder can be attained through heat infusion, spray drying, freeze drying (Chauhan et al. 2013). Since guava juice is very delicate in flavor and usually pink or yellow in colour according to the variety used therefore drying operations need to be carefully designed to preserve the quality and colour. Several methods are used for production of guava powder, but the most successful methods include freeze drying, foam mat drying and spray drying. Although the freeze drying process was successful to convert guava juice into powder the production cost are high (Chopda and Banrett 2004). Hence, spray drying techniques have been applied for producing guava powder Drying by spray drying is cheaper than freeze drying, and the spray dryer capacity is also higher than freeze dryer (Tashtoush et al. 2007). The spray drying is one step process having short dehydration time and controlled pressure in comparison to freeze drying, vacuum drying and tunnel drying which minimizes heat damage (Bhandari et al. 1993). The thermal sensitivity and hygroscopic nature of fruit components gives rise to wall deposition problems and hinders handling procedures. A suitable carrier such as maltodextrin or glucose syrups facilitate drying of fruits like orange, lemon, apricot and mango juices (Ahlawat et al. 2009). This microencapsulation of carrier agents provides longer shelf life and protect against light, oxygen and other type of environmental degradation. It also increases solubility, and improves the handling and flow properties of the core material. Micro-encapsulation has to be optimized several times so that it does not affect the rheological properties or operational events of manufacturing fruit powder (Jafari et al. 2008). However productions of fruit powders by spray drying sustain problems in their functional properties such as stickiness and solubility (Bhandari et al. 1997). Studies suggest that oven drying is a viable option for the production of a functional ingredient that would improve the phenolic content of cereal foods while adding desirable guava flavor (Juliana et al.). More research work is required to overcome the technical difficulties for food processing.

After processing guava remains good source of vitamin C, lipid, ash content and dietary fiber ingredients useful for food industry (De Costa et al. 2009), Products like guava enriched cookies prepared from high fiber obtained from guava waste pulp for ready to product are also equally nutritious (Fátima et al. 2005). Other symbiotic food products guava mousse formed by addition of prebiotic guava fruit and probiotics Lactobacillus acidophilus increases the nutrients of functional foods (Flavia et al. 2010). Consumer awareness is the most important factor determining demand for such type of food products. Sensory analysis and likeability of products increases the market demand. Functional foods offer potential health benefits. Studies aimed at understanding consumers’ needs for functional foods in relation to their traditional diets or special dietary needs are also recommended.

Guava in combination with probiotic fermented dairy food like yoghurt, curd and shrikhand will develop high value commodities to increase application of guava in the area of functional foods (Chauhan et al. 2015). Dairy products such as fermented milks are most popular food of probiotics. They are live microorganisms which when administered in adequate amount confer health benefits. The most common strains of probiotics bacteria are from genus Lactobacillus and Bifidobacterium which are tailored into dietary formulations at global level (Ram et al. 2002). While transferring the probiotics the emphasis for prolonged survival of probiotics in the food matrix is priority. Probiotic bacteria must remain viable in the food carriers and survive the harsh condition of GI tract, with a minimum count of 10⁶CFU/ g^-1 (Kumar et al. 2003). The traditional dairy foods like yoghurt, curd, milk beverages and many more are innovated and manufactured as new probiotic dairy products (Singh, 2001).

Dairy products have been traditionally considered as the best carriers for probiotic bacteria. In recent years, non-dairy probiotic foods have been attracting more attention due to consumer demands. Therefore, in order to alleviate the drawbacks of dairy based probiotics, the development of non-dairy probiotic products, including food matrices from fruit, vegetables, and cereals has a promising future.

Guava (Psidium guajava) pulp was fermented with Lactobacillus plantarum WU-P19 to a product rich in microbially produced vitamin B12 and conjugated linoleic acid (Palachum et al. 2020). In a work by Buriti et al. (2011) pilot-scale mousse were produced and supplemented with Lactobacillus acidophilus La-5 probiotic culture with frozen guava pulp (GP) and prebiotic inulin. Nausheen et al. (2018) reported Guava juice blended with honey and fermentation by different yeasts studied for bioenrichment of guava juice. The results revealed that the guava juice blended with honey as prebiotic and fermented by probiotics of yeast Saccharomyces boulardii showed enriched nutritional. The results concluded that the combined fermentation of guava juice blended with 4 percent honey could be bio-enriched product from guava juice and it will be new product in the food industry.

Psidium guajava is a well-known tropical fruit used in various indigenous systems of medicinal purposes. The multiple disease ameliorating properties of guava, has been discussed in this review. Such properties have been further explained by several studies detailing the specific bioactivity of individual phytochemicals extracted from guava including clinical studies. The ripe guava fruit is a very useful nutraceutical with important properties that can affect the maintenance of health and prevention of many diseases (Hwang et al. 2002). The fruit juices have been proven to prevent diabetes and other metabolic disorders and a potent antioxidant essential for health and well being. Interestingly, this ends pharmacological credence to the implication of designing value added products. Further research is required for characterization and exploitation to innovate guava enriched functional foods.