Starch is one of the most important value-added food ingredients used as a thickener in many foods and industrial applications. This research investigated the effect of different concentrations of starch (anchote and potato) addition on the colloidal stability of pineapple juice. The experiment was carried out on a two-factor factorial design arranged in CRD. The first factor (starch type with two levels (anchote and potato)) and the second factor (starch concentration with three levels (1%, 3%, and 5%)) were considered. The starch-added juice samples were preserved for 15 days at room temperature. The physicochemical properties, colloidal stability, microbial counts, and sensory analysis were conducted in a 7-day interval including the first day. The results revealed that different starch concentrations showed a significant effect (
Pineapple (
Pineapple is a seasonal fruit crop and perishable in nature, and due to the presence of high sugar and moisture contents, postharvest losses during peak harvesting seasons are considerably high (40%) [
A small percentage of insoluble particles (mixture of proteins, pectins, lipids, hemicellulose, cellulose, and other minor components) remain in the cloudy juice processing. Achieving the bright, natural color is not possible in cloudy fruit juices [
Hydrocolloids are used widely in fruits, vegetables, and protein-based juices to improve color or cloud stability for prolonged periods due to their thickening (raising the viscosity) and suspension properties [
Hence, using starch as a stabilizer in fruit juice proves to be vigorous due to its effectiveness, availability, and low in cost. On the other hand, starch does not alter the organoleptic and sensory properties of the juice compared to other hydrocolloids. Researchers reported the use of carboxymethyl cellulose (CMC), low-methoxyl pectin, guar, xanthan, and gellan gum, [
Anchote (
The objective of this research is to determine the effect of potato and anchote starch at 1%, 3%, and 5% on the physiochemical properties, microbial growth, and stability of pineapple juice during short storage durations at room temperatures.
Fully ripened pineapple (Cayenne cultivar) was purchased from the local market of the Bahir Dar City. Anchote (
As the anchote starch was not readily available, isolation and purification were done by Sit et al. [
The experiment was set as
The fully ripened pineapple fruits were washed thoroughly with potable water to remove dirt. The cleaned pineapples were peeled off and cut into pieces with sterile stainless steel kitchen knife. Then, the pineapple pieces were homogenized in a clean electric laboratory disperser (SWFS1.1-00, China). The pineapple juice was filtered through 500
Bulk density of starch samples was determined according to the method of Ohizua et al. [
The WAC of the starch samples was determined by the method of Bello-Pérez et al. [
Swelling power and WSI were determined according to the method described by Bello-Pérez et al. [
The moisture content, ash, crude protein, and fat contents were determined according to the AOAC (2006) method numbers 950.46, 920.153, 992.15, and 989.05, respectively. The total starch content was determined by the AOAC (2007) method number 996.11 [
Amylose and amylopectin contents were determined by using the method of Hassan and Hassan [
Total soluble solid (TSS) content of pineapple juice was measured using a hand refractometer (RX-5000i-Plus, Atago, Tokyo, Japan) (AOAC 2000). 1 ml of a well-homogenized pineapple juice was placed on the prism of a calibrated hand refractometer. The readings were taken, and results were expressed in °Brix.
pH of starch and pineapple juice was determined by using a calibrated pH meter with standard solution of pH 4 and 7. Each sample (10 ml) was taken into a beaker, and then, electrodes of the pH meter (PHS-25/3C, China) were immersed into the sample and the readings were recorded directly (AOAC, 2004).
The titratable acidity (TA) was determined according to AOAC (2004) procedure. 10 ml of sample was taken into a conical flask, and three drops of phenolphthalein indicator were added. The mixture was titrated against 0.1 N NaOH solution. The TA was calculated by the standard formula by using a citric acid titer value and expressed as the citric acid [
Dynamic viscosity of starch and pineapple juice was determined in an Ostwald viscometer (VISCO STAR+H, Spain) at 20°C and expressed in mPa s [
The stability of pineapple juice was assessed by serum cloudiness (turbidity). Cloud stability of the centrifuged samples (4000 rpm for 15 min) (expressed in terms of % light transmission) was determined by measuring absorbance at 660 nm using a UV-Vis spectrophotometer (Agilent Cary 60 UV-Vis spectrophotometer, USA) calibrated with distilled water. The absorbance at 660 nm was directly related to the turbidity of pineapple juice and expressed in nephelometric turbidity units [
The pulp sedimentation of pineapple juice was determined according to the method of Silva et al. [
Vitamin C content was determined by an iodometric titration method as described by Nweze et al. [
Sensory acceptability of pineapple juice was conducted by untrained 20 volunteer panelists (8 females and 12 males) in a hedonic test. The coded pineapple juice samples were presented to panelists randomly for likeness scores on sensory evaluation (taste, flavor, color, consistency, aroma, texture, mouth feel, and overall acceptability) by using a seven-point hedonic rating scale where 7 represents like extremely and 1 represents dislike extremely [
The pineapple juices with different starch levels were stored at ambient temperature for fifteen (15) days. The shelf life of the juice was determined by checking the pH weekly and by determining the microbial growth [
Enumerations of aerobic plate count (APC) and total fungal counts were performed according to the ISO standard method (ISO-4833:2003(E)). Enumeration of APC was done by the serial dilution technique followed by a pour plate method.
At the initial day, 7th day, and 15th day, serial dilution was carried out by taking pineapple juice from each bottle. The serially diluted juice sample (0.1 ml) with dilution factor 103 for fungal enumeration and 104 for bacterial enumeration was plated and incubated at 37°C for 24 h for bacteria and for fungi at room temperature for 72 h. The colonies from bacteria were counted using the colony counter. The mean value of the triplicate was taken, and the number of colonies was multiplied by the dilution factor and calculated as 1 ml of original sample. It was then expressed as colony-forming unit per ml (cfu/ml) of the sample [
A triplicate data was subjected to analysis of variance (ANOVA) using Minitab version 19.2. Analysis of variance was performed with the general linear model. The mean separation was done by the Tukey method and considered a significant difference at
The results on physicochemical and functional properties of the potato and anchote starches are given in Table
Functional and physicochemical properties of potato and anchote starch.
Starch sample | Bulk density (g/cm3) | WAC (g/g) | WSI (g/g) | Swelling power (%) | Viscosity (mPa s) | pH |
---|---|---|---|---|---|---|
Anchote | ||||||
Potato | ||||||
Values are presented as the
A significant difference (
The mean WAC of 1.4 g/g and 1.1 g/g was observed for potato and anchote starch, respectively. The highest WAC of potato starch could be attributed to the presence of higher amount of carbohydrates (starch) and fiber. The fibers have good ability to associate with water under limited water presence (high hydration properties) [
The SP showed 4.9% for potato starch, whereas 6.2% for anchote starch. The capacity to hydrate and swelling allows changes in starch viscosity. The higher amylopectin content is responsible for higher SP and viscosity at low temperatures. The swelling capacity of starch granules allows increasing their viscosity and gelling properties [
The WSI values of the starches were 1.2 g/g and 0.6 g/g for potato and anchote, respectively. WSI measures the number of free molecules leached out from the starch granules in addition to excess water and thus reflects the extent of starch degradation [
The mean viscosity values were observed as 235.3 mPa s and 241.7 mPa s for potato and anchote starches, respectively. The higher viscosity was observed for the anchote starch. The results of pH for starch samples were reported as 6.0 and 6.1 for potato and anchote starch, respectively. The pH values of the starch in water suspension are important because some functional properties like solubility and emulsion properties are highly affected by change in pH [
Analysis of variance showed significant difference (
Proximate composition and amylase and amylopectin contents of starch from anchote and potato tubers.
Starch sample | Moisture (%) | Ash (%) | Fat (%) | Starch (%) | Protein (%) | Amylose (%) | Amylopectin (%) |
---|---|---|---|---|---|---|---|
Anchote | |||||||
Potato | |||||||
Values are presented as the
The crude protein contents of potato and anchote starches were 0.30% and 0.4%, respectively. The protein contents of starches were similar as previously reported by Abera et al. [
The total starch contents in potato and anchote starches were observed as 89.7% and 76.3%, respectively. The value of potato starch content was similar with the value reported by Abera et al. [
The amylose contents in potato and anchote starches were 25.7% and 15.8%, respectively. Similar amylose content in potato starch has been reported by Sanchez-González et al. [
The amylopectin contents in potato and anchote starches were 75.8% and 84.5%, respectively. Similar amylose content in potato starch has been reported by Sanchez-González et al. [
The results on the physicochemical properties of pineapple juice as a function of storage time are given in Table
Physicochemical properties of pineapple juice samples added with different types of starch with different concentrations stored for 15 days.
Storage time (days) | Juice sample | Sedimentation (%) | TSS (%) | pH | Viscosity (mPa s) | Turbidity (FTU) | TA (%) | Vitamin C (mg/100g) |
---|---|---|---|---|---|---|---|---|
Initial day | Control | — | ||||||
AS1 | — | |||||||
AS3 | — | |||||||
AS5 | — | |||||||
PS1 | — | |||||||
PS3 | — | |||||||
PS5 | — | |||||||
Day 7 | Control | |||||||
AS1 | ||||||||
AS3 | ||||||||
AS5 | ||||||||
PS1 | 1 | |||||||
PS3 | ||||||||
PS5 | ||||||||
Day 15 | Control | |||||||
AS1 | ||||||||
AS3 | ||||||||
AS5 | ||||||||
PS1 | ||||||||
PS3 | ||||||||
PS5 | ||||||||
Initial day | — | |||||||
Starch type | — | |||||||
Starch concentration | ||||||||
Day 7 | ||||||||
Starch type | ||||||||
Starch concentration | ||||||||
Starch type | Day 15 | |||||||
Starch type | ||||||||
Starch concentration |
Values are presented as the
Pineapple juices with potato starch showed higher sedimentation than juice with anchote starch. The control samples showed highest degree of sedimentation as compared to starch-added samples during the storage time. The sedimentation and phase separation were observed in the first 24 h of stored control samples; it is a common behavior of some fruit juices [
As the storage time increased, the sedimentation also increased; in contrast, as the starch concentration increased, the sedimentation decreased in the first 7 days of storage while increased after 7 days of storage. This may be due to the increase in concentration of starch that leads to the settlement of cloud. It has been reported that incorporation of starch with higher concentrations leads to a higher electrolyte concentration, resulting in salting out of the starch [
The sedimentation decreased significantly (
Analysis of variance (Table
The effect of interactions and main effects was significant (
The ANOVA showed that pineapple juices exhibited a slight increase in the TA over storage time and were significantly varied (
The ANOVA showed that the effect of interactions was not significant on TSS of pineapple juice at
The analysis of variance revealed that TSS of pineapple juices slightly decreased over storage durations and were not significantly varied (
There was no significant (
The ANOVA showed that the viscosity of pineapple juice significantly (
This tread may be attributed to the degree of starch polymerization. With a high degree of polymerization, the solution viscosity will be high. The results of the present study are in agreement with the findings of Shamsudin et al. [
The statistical analysis showed that the effect of interactions and main effects was significant on the turbidity of pineapple juice at
The turbidity of the pineapple juice decreased significantly (
The cloud retention in pineapple juice was significantly improved by the addition of starch. As studies reported, juice cloudiness occurs mainly due to the suspension of solid particles [
According to the Stokes law, the larger-sized particles are easier to precipitate. A good thickener can prevent the formation of large polymers. The difference in absorbance values was mainly influenced by the particles that remained in suspension [
The results of sensory acceptability of pineapple juices as a function of storage time are presented in Figure
Sensory acceptability of pineapple juice. (a) Initial day. (b) Stored for 7 days. Control: pineapple juice (without starch); AS1: 1% anchote starch; AS3: 3% anchote starch; AS5: 5% anchote starch; PS1: 1% potato starch; PS3: 3% potato starch; PS5: 5% potato starch.
Subsequently, aroma, flavor, and mouth feel of juice are the most important factors that affect the pineapple juice acceptability; all consumers like pineapple juice with good flavor, mouth feel, and aroma. In terms of the texture, it is also an important factor; generally, soft texture is easy to accept by humans. Overall, acceptance of the juices with starch is important because consumers are not interested in consuming pineapple juice which is not in good appearance.
The effect of storage time, type, and amount of starch on the total viable bacterial and fungal counts of pineapple juice during storage is illustrated in Figure
Microbial load of pineapple juice stored for 15 days. Control: pineapple juice (without starch); AS1: 1% anchote starch; AS3: 3% anchote starch; AS5: 5% anchote starch; PS1: 1% potato starch; PS3: 3% potato starch; PS5: 5% potato starch; PCA (B): total bacterial count; PDA (M): total fungi count.
The results revealed that the total bacterial and fungal count in all pineapple juices increased throughout the storage time. However, increased starch concentration had a significant decreasing effect on the microbial content compared with the control juice during storage. In general, control sample showed remarkably high microbial loads during the period of storage and this may be possibly a major cause of spoilage commonly experienced by the producers of this product [
The results of this study revealed that addition of potato and anchote starch significantly improved the cloud stability of the pineapple juice as compared to the control. The findings showed that starch type and starch concentration levels had significantly influenced some of the physicochemical parameters (turbidity, viscosity, and sedimentation) and microbial content of the pineapple juice in comparison to the control. Moreover, storage time had significant influenced on turbidity, viscosity, sedimentation, and microbial counts of the stored pineapple juice. As starch concentration in the juice increased, minimum influence on vitamin C content, TSS, TA, and pH of juice was observed. With increasing in storage time, turbidity, viscosity, TSS, pH, and vitamin C content of juice decreased, whereas sedimentation, TA, and microbial counts were increased. Adding starch with different concentrations had not significantly influenced the sensory acceptability of pineapple juice, even though there were some changes observed for some sensory attributes. In general, the findings showed that addition of starch with different concentrations had significantly influenced some physicochemical and shelf life of pineapple juice as a function of time.
The result showed that pineapple juice with 5% anchote starch had better cloud stability during storage period. This is because of product exhibited less pulp sedimentation and high viscosity and turbidity. Generally, addition of 5% starch helped in maintaining the cloud stability, reduction in microbial load, and no influence on the sensory acceptability of the pineapple juice over a period of 15 days.
The data used to support the findings of this study are included within the article.
None of the authors showed any conflict of interest.
We express our gratitude to the technical and academic staff of the Laboratory of Food Processing for their pieces of advice and support and for providing us with all the necessary facilities to carry out this study. Sincere indebtedness also goes to individuals that have participated in the sensory evaluation of the pineapple juice samples.