Physical quality of goat milk yogurt with the addition of pineapple and purple sweet potato

It is necessary to eliminate the rancid smell of goat milk by fermentation technology through yogurt-making plus pineapple juice and purple sweet potato juice stabilizer. Adding pineapple juice and purple sweet potato is a food diversification by utilizing agricultural production and maintaining environmental sustainability. The study sought to enhance consumer enthusiasm for ingesting goat milk yoghurt by incorporating pineapple juice and purple sweet potato. This study used a factorial experiment in RAL 3 x 3 with 3 replications. Factor I pineapple juice dose consists of N1 = 5%, N2 = 10%, and N3 =15%. Factor II dose of purple sweet potato juice consisted T1: 0.2% (T1), T2: 0.4% and T3: 0.6%. Control goat milk yogurt without adding pineapple and purple sweet potato juice. The parameters studied consisted of. swell ability and solubility, syneresis, viscosity and WHC (Water Holding Capacity). The results of the study the addition of 15% pineapple juice (N3) and 0.6% purple sweet potato (T3) produced the best physical quality of goat milk yogurt increasing the swelling power, solubility, water holding capacity, viscosity with respective values of 10.73%, 3.08%, 90%, and 352.93% and decreasing syneresis with a value of 15.73%.


Introduction
Need to reduce the rancid odour of goat milk with fermentation technology.The yogurt produced so far has a sour taste because it uses a mixed starter of S. thermophilus and L. Bulgaricus.Research is needed to use a single starter to reduce the sour taste of yogurt.A single starter that can be used in making yogurt is the Pediococcus pentosaceus Strain N6 isolate.This isolate was isolated from the hot springs of Rimbo Panti, West Sumatra.Isolates can grow at temperatures of 45-500C, pH grows 2 to 8 and an optimum pH is 3 to 7, and have high antimicrobial activity against Listeria monocytogenes bacteria [1].Furthermore, according to [2], these isolate produces metabolism in the form of lactic acid and bacteriocin Pediocin N6 so this isolate has high antimicrobial activity against pathogenic bacteria Listeria monocytogenes which can grow at cold temperatures.
In making yogurt, it is necessary to add fruit to improve the flavour.One of the fruits that can be added is pineapple.Pineapple is an agricultural production that is widely grown by the community, but its utilization has not been maximized.It is necessary to use pineapple as a local Indonesian resource as a flavour enhancer in making yogurt.Pineapple has a distinctive aroma that is favoured by the public and has health benefits so that it can function as a functional food.The pineapple fruit is rich in essential nutrients including calcium, potassium, vitamin C, carbohydrates, crude fibre, water, as well as a variety 1302 (2024) 012102 IOP Publishing doi:10.1088/1755-1315/1302/1/012102 2 of minerals, vitamins, flavonoids, polyphenols, and saponins.These compounds function as antioxidants and antibacterial agents [3].
The yoghurt produced thus far has subpar quality due to its limited water binding capacity, resulting in whey separation.The reason for this is that the pH of yoghurt falls within the range of the isoelectric point of casein.At the isoelectric pH, the casein gel has a limited ability to bind water molecules, which promotes the release of water molecules from the gel's surface.This process, known as syneresis, leads to a drop in viscosity [4].In order to enhance the quality of yoghurt, it is imperative to incorporate a stabiliser, specifically purple sweet potato.Sweet potato is among the several agricultural commodities in Indonesia.According to the statistics from reference [5], the total output of purple sweet potatoes in 2015 amounted to 2,261,124 tonnes, with a productivity rate of 160.53 quintals per hectare.The abundant supply of purple sweet potato should be harnessed to promote food diversification and leverage local resources in the manufacture of yogurt.
Inulin can act as a stabilizer or fat replacer due to its ability to bind water molecules to form a network of gel particles.Natural inulin comes from wheat, asparagus, garlic, leeks, onions, Jerusalem artichokes, and chicory [6].The use of inulin as a prebiotic aims to obtain fermented products that have a positive impact on health and have antioxidant activity.[7], stated that purple sweet potato has a Fructo Oligo Saccharide (FOS) content of 0.39% and α-inulin 0.33% and serves as a source of substrate for the growth of probiotic bacteria.Purple sweet potato also contains anthocyanins, natural colour substances that function as antioxidants that can prevent atherosclerosis, which is a blockage of blood vessels.
The objective of this study is to investigate the impact of incorporating pineapple juice and purple sweet potato into the production of yogurt, using a specific strain of bacteria called Pediococcus pentosaeus Strain N6.The goal is to enhance the physical characteristics of goat milk yogurt and generate public interest in it, by utilizing agricultural resources and natural ingredients.

Research Materials
2.1.1.Making Pineapple Juice.In the modified method of [8], ripe pineapple (Ananas comosus) was peeled, washed, and sliced into small sizes then the core of about 10-15 mm was removed.Next, it is blended, after which filtering is done with a filter cloth to obtain pineapple fruit extract.The pineapple fruit extract was pasteurized by heating at 90 -95°C for 5 minutes, Subsequently, the substance was chilled and preserved in a refrigerator in a temperature range of 4 -6°C till it is ready for utilization.

Making Purple Sweet Potato
Juice.Modified method of [9], purple sweet potato weighed 300 g and then peeled and washed thoroughly.Purple sweet potato was sliced into small cubes, 300 ml of water was added, and then placed in a blender to produce sweet potato pulp.The sweet potato pulp was poured into a glass jar using a funnel lined with filter cloth and allowed to stand for 15 minutes then the filtrate was taken.This phosphate is ready to be used to make yogurt.

Refreshment of Pediococcus pentosaceus Strain N6
Isolate.The thermophilic lactic acid bacteria (LAB) strains were cultivated on a medium specifically designed for methicillin-resistant Staphylococcus aureus (MRSA) and thereafter subjected to incubation at a temperature range of 45-50oC for a duration of 24 hours.Subsequently, a solitary quantity of a thermophilic LAB isolate was cultivated in 9 ml of MRS broth medium and subsequently subjected to incubation at a temperature range of 45-50oC for a period of 24 hours.The liquid culture of Pediococcus pentosaceus isolate Strain N6 has been developed and is currently accessible for use in the manufacturing of yoghurt [1].

Making Yogurt Starter.
In the modified method of [10], the strain was activated by pouring 200 ml of goat's milk (1 drinking glass) into a pot and adding 5-10% sugar (2 tablespoons), then heating at 70-80 0 C for 5-10 minutes.A small glass bottle with a lid was prepared and sterilized by putting boiling water into the bottle for a few minutes, then the water was immediately discarded and the bottle was tightly closed.The heated milk was put into bottles of 100 ml each and waited until the temperature dropped to around 40-45 0 C (lukewarm).In each bottle, 5% (3-5 ml) of Pediococcus pentosaceus Strain N6 isolate was inoculated and then incubated at 45-50°C for 24 hours.After that, it is ready to be used as a yogurt starter.

Preparation of Flavoured Goat Milk Yoghurt with the Addition of Sweet Potato Juice and
Pineapple.Modified method [11], fresh goat's milk was placed in 54 glass bottles with lids each containing 100 ml then pasteurized at 70-80°C for 5 minutes, added sugar as much as 6.5% (b/v).Goat milk was then cooled and placed in laminar flow, The yogurt starter culture and extracts of purple sweet potato and pineapple were introduced at an inoculation temperature of 42-45°C, following the specified protocol, and subsequently homogenized.Subsequently, it underwent incubation at a temperature range of 45-50 o C for 18 hours.

Research methods
The experiment employed a fully randomized design with a 3 x 3 factorial arrangement, and each treatment combination was replicated three times.The initial variable was the concentration of purple sweet potato juice, which included 0.2% (T1), 0.4% (T2), and 0.6% (T3).The second element comprises three different doses of pineapple juice: 5% (N1), 10% (N2), and 15% (N3).Regulate the production of goat's milk yogurt without incorporating pineapple and sweet potato juice.

Syneresis.
The method according to [11], The specimen was measured to be 0.2 grams or 2% by volume, subjected to heating at a temperature of 85 o C for 30 minutes, and subsequently centrifuged at a speed of 3200 revolutions per minute for 15 minutes.The liquid component was extracted and the resulting extract was measured by weight.[12], 10 ml of yogurt sample was put into the viscometer, then sucked with a rubber ball until it reached the upper limit.the sample flow time was calculated to reach the lower limit and repeated 3 times.

Water Holding Capacity (WHC)
. Method according to [13], 1 gramme sample was subjected to centrifugation at a speed of 16,000 revolutions per minute for a duration of 15 minutes at a temperature of 25 degrees Celsius.The liquid portion was eliminated within a time frame of less than 10 minutes, and the weight of the moist solid residue was measured.The expression of WHC is as follows. (1)

Swelling Power and Solubility.
Method according to [13], a 0.1 gramme portion of yoghurt was combined with 10 millilitres of distilled water and subjected to centrifugation at a speed of 3000 revolutions per minute for a duration of 20 minutes.Subsequently, the solubility and expandability of the mixture were examined.

Data analysis
The data were assessed using Analysis of Variance (ANOVA) to determine if there was a statistically significant difference between the treatments.If a significant difference was found, further analysis was conducted using Duncan's test.The data was analysed using SPSS 20 software, with a significance threshold of 5% (p<0.05).

Syneresis
The mean syneresis value of a singular starter goat milk yogurt isolate, specifically the Pediococcus pentosaceus strain N6, with the inclusion of purple sweet potato and pineapple juice, as presented in Table 1 below: Result of the analysis of the variance test with SPSS, there was a very significant interaction (P<0.05) between the doses of purple sweet potato juice and pineapple on the decrease in yogurt syneresis likewise, the effect of starter dose alone and incubation duration alone.The results of Duncan's further test (Table 1), the treatment of 1.2% purple sweet potato dose (T3) and 9% pineapple (N3) or T3N3, showed a very significant interaction (P<0.05) with other treatments with a value of 15.73%.The dose of 1.2% purple sweet potato juice (T3) alone showed a very significant effect (P<0.05) in reducing yogurt syneresis against the other treatments with a syneresis value of 21.9%.The dose of pineapple juice 9% (N3) alone, showed a highly significant impact (P<0.05) to reduce yogurt syneresis against other treatments with a syneresis value of 33.67%.
The interaction effect of adding the dose of purple sweet potato 1.2% (T3) and pineapple 9% (N3) or T3N3, shows a very significant interaction that reduces yogurt syneresis because according to [9], increasing water binding capacity results in increased viscosity which results in reduced whey separation or syneresis in the fermented product.
The addition of 1.2% purple sweet potato juice (T3) has a highly significant impact on reducing yogurt syneresis.This is because the purple sweet potato juice contains starch, which acts as a thickener or stabilizer.As a result, the viscosity of goat milk yogurt increases, leading to a lower amount of water being released from the yogurt (syneresis).As stated in reference [3], augmenting the concentration of thickeners in fermented products enhances their water retention capacity, hence reducing the amount of water released from the gel or syneresis.
The effect of adding 9% pineapple juice dose (N3) alone showed a very significant effect on reducing yogurt syneresis because the addition of pineapple juice containing organic acids and bromelain enzymes resulted in an increase in the acid content and bromelain enzymes in goat milk, the acid content and bromelain enzymes resulted in increased clumping of milk proteins so that the yogurt syneresis value decreased.According to [14], bromelain enzyme has hydrolysis properties such as protease enzymes.The enzyme is proteolytic which has a high ability to break peptide bonds so that it can coagulate milk proteins.Increased milk clumping will decrease yogurt syneresis.

Viscosity
The mean viscosity measurement of a specific strain of Pediococcus pentosaceus (N6) isolated from goat milk yogurt starter, when combined with purple sweet potato juice and pineapple, is presented in Table 2.The analysis of the variance test conducted with SPSS revealed a highly significant interaction (P<0.05) between the dosages of purple sweet potato and pineapple juice to the increase in yoghurt viscosity.Similarly, the impact of the first dosage alone and the time of incubation alone.The additional test findings conducted by Duncan (as shown in Table 20) revealed a highly significant interaction (P<0.05) between the treatment including 1.2% purple sweet potato (T3) and 9% pineapple (N3), denoted as T3N3.This interaction resulted in a viscosity value of 352.93%.The administration of 1.2% purple sweet potato juice (T3) had a highly significant impact (P<0.05) on increasing the viscosity of yoghurt compared to the other treatments, resulting in a value of 326.82%.The administration of pineapple juice at a concentration of 9% (N3) had a highly significant impact (P<0.05) on raising the viscosity of yoghurt compared to other treatments, resulting in a 215.14% increase.
The interaction effect of adding a dose of purple sweet potato 1.2% (T3) and pineapple 9% (N3) or T3N3, showed a very significant interaction that increased the viscosity of yoghurt because according to [15], the addition of stabilizing agents will increase viscosity.The rise in viscosity is attributed to the incorporation of sweet potato starch, which acts as a thickening agent, and pineapple juice, which enhances the aggregation of milk protein.An increased concentration of thickener leads to the agglomeration and augmentation of the viscosity of goat milk.
The impact of elevating the dosage of purple sweet potato extract to 1.2% (T3) in isolation exhibits a highly notable effect on augmenting the viscosity of goat's milk yoghurt.This is due to the presence of starch, composed of amylose and amylopectin, within the purple sweet potato extract.Additionally, the extract contains carbohydrates that serve as stabilizers.Raising the concentration of stabilizers in goat's milk will enhance the thickness or viscosity of the yogurt.As stated in reference [16], augmenting the thickening agent leads to a rise in water retention capacity, increasing viscosity.In addition, elevating the levels of amylose and amylopectin induces the formation of crystallization, resulting in a denser consistency of the yogurt.
The addition of 1.2% purple sweet potato juice (T3) had a pronounced impact on enhancing the viscosity of goat milk yoghurt.This is attributed to the presence of starch, composed of amylose and amylopectin, in purple sweet potato juice.Additionally, the juice contains carbohydrates that act as stabilizers.Elevating the concentration of stabiliser in goat's milk will result in a corresponding increase in the viscosity of the yogurt.As stated in reference [16], augmenting the concentration of the thickening agent leads to a corresponding rise in water retention capacity, increasing viscosity The addition of a 9% dose of pineapple juice (N3) had a highly significant impact on increasing the viscosity of yoghurt.This is due to the presence of organic acids and the proteolytic enzyme bromelain in pineapple juice, which causes the milk protein to clump together, increasing yoghurt viscosity.As stated in reference [17], pineapple juice includes the proteolytic enzyme bromelain.This enzyme can break peptide bonds, causing milk protein or casein to coagulate.This process increases the viscosity of the mixture and enhances the texture of yoghurt.

Water Holding Capacity (WHC)
The mean water holding capacity of a single strain of Pediococcus pentosaceus (N6) in goat milk yogurt, supplemented with purple sweet potato juice and pineapple, is presented in Table 3.The analysis of variance test conducted using SPSS revealed a highly significant interaction (P<0.05) between the dosages of purple sweet potato juice and pineapple in relation to the increase in water retaining capacity of yoghurt.The additional test findings conducted by Duncan (as shown in Table 21) revealed a highly significant interaction (P<0.05) between the treatment including 1.2% purple sweet potato (T3) and 6% pineapple (N2), or T3N2.This interaction resulted in a substantial increase in the water holding capacity of yoghurt, with a value of 90.0%.The administration of 1.2% purple sweet potato juice (T3) had a highly significant impact (P<0.05) on raising the viscosity of yoghurt compared to other treatments, resulting in a value of 88.07%.The inclusion of pineapple juice alone did not have a statistically significant impact (P>0.05) on the water-holding capacity of yoghurt.
The interaction effect of adding a dose of 1.2% purple sweet potato (T3) and 6% pineapple (N2) or T3N2, showed a very significant interaction that increased the water-holding ability of yoghurt because according to [18], purple sweet potato contains starch, so the increase in starch in milk will increase the viscosity while increasing the water-holding ability of yogurt.
The addition of a dose of 1.2% purple sweet potato juice (T3) alone, showed a very significant effect on increasing the water-holding ability of yoghurt because purple sweet potato contains starch which is a complex carbohydrate that can bind water, so an increase in starch content in goat milk will increase the viscosity of yoghurt so that the ability of yoghurt to hold water will increase.According to [19], an increase in starch-containing ingredients will increase the water-holding ability of yogurt because starch granules will experience swelling in absorbing water in yogurt so that viscosity increases.

Swelling Power
The mean expandability of a singular starter goat milk yogurt isolate Pediococcus pentosaceus strain N6, when combined with purple sweet potato juice and pineapple, as displayed in Table 4  Note: Numbers with superscripts in the same row and column show no significant difference (P>0.05).Meanwhile, numbers with different superscripts show a very significant effect (P<0.05).
The analysis of the variance test conducted using SPSS revealed a highly significant interaction (P<0.05) between the dosages of purple sweet potato juice and pineapple about the increase in yoghurt expandability.Similarly, the impact of the dosage of purple sweet potato juice in isolation and pineapple juice in isolation.The findings of Duncan's additional experiment (Table 22) demonstrated a highly significant interaction (P<0.05) between the treatment of 1.2% purple sweet potato (T3) and 9% pineapple (N3), or T3N3.This interaction led to a substantial increase in yoghurt expandability compared to other treatments, with a value of 10.73%.The administration of 1.2% purple sweet potato juice (T3) had a highly significant impact (P<0.05) in enhancing the expandability of yoghurt compared to other treatments, resulting in a 10.48% increase.The administration of pineapple juice at a concentration of 9% (N3) had a highly significant impact (P<0.05) on enhancing the blooming ability of the yoghurt compared to other treatments, resulting in a 9.14% increase.
The combined effect of adding 1.2% purple sweet potato juice (T3) and 9% pineapple (N3), or T3N3, resulted in a highly significant interaction that enhanced the growth of yoghurt.This is attributed to the presence of carbohydrates in the form of starch in purple sweet potato.Starch is a complex mixture of amylose and amylopectin, which are arranged in a structured manner inside starch granules.Expansion arises from the formation of non-covalent links between starch molecules.The starch granules will undergo further expansion, resulting in an increase in viscosity until reaching the maximum hydration volume.Augmenting the quantity of sweet potato juice in milk will elevate the concentration of starch in milk.Similarly, escalating the dosage of pineapple juice leads to an upsurge in organic acids in milk, consequently augmenting the viscosity of milk protein.An elevation in milk viscosity leads to a corresponding rise in yogurt expandability.As stated in reference [13], a greater concentration of starch leads to an increased expandability value due to the presence of amylose and amylopectin, which are responsible for water absorption during heating.The integrity of amylopectin is crucial for both the swelling power and the shape of granules.
The addition of 1.2% purple sweet potato extract (T3) alone had a remarkably substantial effect on increasing the swelling capacity of yoghurt.The reason for this is the existence of starch, which is made up of amylose and amylopectin, in the extract of purple sweet potato.Therefore, incorporating purple sweet potato extract into goat's milk results in an enhancement in gelatinization and a rise in the swelling power of yogurt.According to [20], amylose and amylopectin are essential in the formation of starch paste and gel.Moreover, higher amounts of amylopectin and starch lead to the creation of elongated gel chains that demonstrate improved viscosity and stability.The ability of starch to swell is due to the noncovalent interactions between starch molecules.
The inclusion of 1.2% purple sweet potato juice dose (T3) independently demonstrated a highly significant impact on enhancing the expandability of yoghurt.This is attributed to the presence of starch, specifically amylose and amylopectin, in purple sweet potato juice.Consequently, the addition of purple sweet potato juice to goat's milk leads to the formation of a more gelatinous structure and an increased ability of the yogurt to expand.As stated by [20], amylose and amylopectin play a crucial role in the creation of starch paste and gel.
The inclusion of 9% pineapple juice dose (N3) independently exhibited a highly significant impact on enhancing the swell ability of yoghurt.This is due to the presence of carbohydrates, including sugars and organic acids, in pineapple juice.Elevated levels of lactic acid in goat's milk lead to heightened aggregation of milk proteins, resulting in an augmented viscosity of the yogurt.An increase in yogurt viscosity will enhance its water retention capacity and expandability.As stated in reference [8], augmenting the number of starter cells in the fermentation process will enhance the yogurt's capacity to retain water, particularly during the gelatinization phase.There is a favourable correlation between low slurry density and high expandability.The fermentation process creates a porous structure in the yogurt, which decreases the density of the mixture.

Solubility
The mean solubility value of an individual starter isolates of goat milk yogurt, namely the Pediococcus pentosaceus strain N6, when combined with purple sweet potato juice and pineapple, is presented in Table 5.The analysis of variance conducted using SPSS revealed a highly significant interaction (P<0.05) between the dosages of purple sweet potato juice and pineapple to the increase in yoghurt solubility.Similarly, the individual effects of purple sweet potato juice and pineapple juice alone were also seen.The findings from Duncan's additional test (Table 5) indicate that the combination of a 1.2% dose of purple sweet potato (T3) and a 9% dose of pineapple (N3), or T3N3, had a highly significant interaction (P<0.05).This interaction resulted in a substantial increase in the solubility of yoghurt compared to other treatments, with a value of 3.20%.The administration of 1.2% purple sweet potato juice (T3) had a notable impact (P<0.05) on enhancing the solubility of yoghurt compared to other treatments, resulting in a value of 3.08%.The administration of pineapple juice with a concentration of 9% (N3) had a highly significant impact (P<0.05) on enhancing the solubility of yoghurt compared to other treatments, resulting in a solubility increase of 2.42%.
The combined effect of adding 1.2% purple sweet potato juice (T3) and 9% pineapple (N3), referred to as T3N3, had a highly significant impact on the solubility of yoghurt.During the fermentation of goat's milk, the microbial starter will use the starch in sweet potato juice and organic acids from pineapple juice as nutrients to break down the milk into glucose.The solubility of yoghurt can be enhanced by increasing the dosage of purple sweet potato juice and pineapple due to glucose's highwater solubility.As stated in reference [13], fermentation involves the breakdown of starch bonds, resulting in a simpler structure.Additionally, a portion of the starch is converted into glucose, which enhances its water solubility.

Conclusion
Goat milk yogurt fermented with Pediococcus pentosaceus Strain N6 isolate and then added with 15% pineapple juice (N3) and 0.6% purple sweet potato juice (T3) improved the physical quality of goat milk yogurt.The addition of pineapple juice and purple sweet potato juice increased expandability, solubility, water-holding ability, and viscosity with values of 10.73%, 3.08%, 90%, and 352.93% respectively, and decreased syneresis with a value of 15.73%.The addition of pineapple juice and purple sweet potato juice in making goat milk yogurt is an effort to utilize agricultural and livestock production through food diversification and preserve natural resources and the environment.

Table 1 .
Average Syneresis Value of Yoghurt Interaction with Additional Doses of Purple Sweet Potato and Pineapple Juice Note: Numbers with superscripts in the same row and column show no significant difference (P>0.05).Meanwhile, numbers with different superscripts show a very significant effect (P<0.05).

Table 2 .
Average Yogurt Viscosity Value Interaction with Additional Dosage of Purple Sweet Potato Juice and Pineapple.Note: Numbers with superscripts in the same row and column show no significant difference (P>0.05).Meanwhile, numbers with different superscripts show a very significant effect (P<0.05).

Table 3 .
Mean Value of Water Retaining Capacity of Yogurt Interaction Dose Addition of Purple Sweet Potato and Pineapple Juice.

Table 4 .
below: Mean Yoghurt Rise Value of Interaction Dose Addition of Purple Sweet Potato and Pineapple Juice.

Table 5 .
Mean Yogurt Solubility Value of Interaction Dose Addition of Purple Sweet Potato and Pineapple Juice.