Isolation of Potato Peel Starch & Its Food Application

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1. Introduction

Potatoes Solanum tuberosum is one of the largest grown crops not only in Pakistan but in the entire world. At present China is the largest potato producer in the world that has an output of 72,000,000 tons followed by India. India produces about 26,280,000 tons. (Debdatta, 2020).In Pakistan potato was grown on 0.184 million hectares with a production of 4.142 million tonnes (FAOSTAT, 2019). Potato peel constitute about 11.2 % moisture, ash 7.5 %,sugars 3.4%,carbohydrates 64.47 %,& protein 13.2 % by dry weight.

China is the largest potato producer in the world that has an output of 72,000,000 tons followed by India. India produces about 26,280,000 tons. (Debdatta, 2020). In Pakistan potato was grown on 0.184 million hectares with a production of 4.142 million tonnes (FAOSTAT, 2019).

This study is aimed at isolation of starch from potato peel. When a person eats a starchy item of food the gut does not necessarily digest all of it. At time the starch passes through human’s gut without being broken. Such a starch that resists digestion is labeled as resistant or active starch.

Resistant starch has a high amylose content in it. It does not get digested in small intestine rather it gets fermented in large intestine. Resistant starch gives a feeling of fullness which means it adds to the satiety value of food. Furthermore it does not spike up the blood glucose levels. The good bacteria in the gut start to proliferate due to resistant and active starch. (Gunar, 2018).A starch which is high in amylose content improves insulin sensitivity (World Health Organisation, 2015). The aim of this study is to isolate potato peel starch, modify by autoclaving and its supplementation in oatmeal cookies. Starch is extracted through alkali steeping & resistant starch is produced via autoclaving. A cookie may add up to 160 calories in a diet with protein 1g, carbohydrates 25 g & fiber 1.2 grams. (M Scott, 2010).

2. Methods

2.1. Isolation of potato peel starch

Potato peel starch was isolated through the help of alkali steeping method Madson’s method (Deepa, 2013).It was used with a slight modification. This method was proposed in 2010. Percentage yield of starch was calculated by making use of the formula as mentioned below Percentage yield = (dry weight of starch x 100) / dry weight of ground potato peel powder

2.1.1. Optimization of isolation process

The method of isolation of starch was optimized by changing amplitude & time durations of ultrasonication through the assistance of sonicator. Absorbance of the solution was taken by spectrophotometer at 620nm.

2.1.2. Modification of starch

The starch was modified using the method of Nasrin (Taslima Ayesha, 2014).Potato peel starch was at first dissolved in distilled water (1:10 w/w) with a pH of 7.5. The starch was autoclaved at 130°C & cooled down at 4° for a day. This was done three times.

2.2. FTIR (Fourier Transform Infrared)

FTIR analysis was done by using Cary 630, Agilent Technologies. Wavenumber range of the measurements taken was 500 to 4000 cm-1.

2.3. Water solubility index & Water absorption index

Based on the method of gerçekaslan (2020) the water absorption index of the samples of starch was determined. • The formula used to calculate water solubility index (WSI) is mentioned below:

Water solubility index = Weight afterwards drying method / weight of actual starch sample • The formula used to calculate water absorption index is mentioned below:

Water absorption index = Weight of wet sediment / Dry weight of actual starch sample

2.4. Swelling Power

Calculation of swelling power was done through the method proposed by (Moses, 2018).The swollen paste from the clear supernatant was also weighed through with the help of weighing balance.

The swelling power was calculated using the formula mentioned below:

Swelling Power =Weight of the (swollen) paste / Weight of dry starch

2.5. The determination of amylose content

For the determination of amylose content iodine calorimetric method was used (Khoomton & Noomhorn, 2015). Standard curve was formulated to determine the exact amylose content.

2.6. Oatmeal Cookies Preparation

0, 1% & 5 % modified starch was added in oatmeal cookie dough with jaggery & gram flour. Dough was kneaded was only 5 minutes & then cooled at 4° for 2 hours.(AllRecipe.com)

2.6.1. Proximate Analysis

Protein,Fat,NFE content of oatmeal cookies alongwith moisture & ash content of oatmeal cookies was determined.

2.6.2. Texture Analysis

Texture of cookies was analysed through a texture analyzer.

2.6.3. Sensory Evaluation

A 9 point hedonic scale was used for sensory evaluation by a panel consisting of 25 respondents.

2.7. Assessment of modified starch prebiotic effect

The strains of Pediococcus bacterium and Bifidobacterium were propagated at 37°C using Man Ragos Broth (MRS) broth for 24 hours. After sub culturing, these were grown in various concentrations of modified starch (0%,1% and 2%).

2.8. Enzyme Hydrolysis

Through amylase enzyme hydrlysis of modified starch was done.( Babatunde, 2023).

2.9. Acid Hydrolysis

Through Hydrochloric acid hydrolysis of modified starch was done by making use of DNS Reagent. (Shujun Wang, 2015).

3. Results

3.1. Starch Yield

Starch extracted from potato peel with total yield of 49.35 % (w/w) was termed as unmodified starch (UMS).Modified starch was prepared by autoclaving. Total modified starch yield was 29.95% (w/w).Treated modified starch was termed as (M.S).

UMS MS Fig 1: Unmodified starch & modified starch

3.2. Optimisation of Starch Yield

To detect maximum yield of starch sonication time & amplitude was continously altered with variations in sample to solvent ratio.

Table 1: Optimisation of starch yield Sample (gm) Sonication Time 10 Sec ON 20 Sec OFF Amplitude % Volume of Solution (ml)

Concentration Of Starch (gm)

3.3. Fourier Transform Infrared Spectra of Unmodified

& modified starch FTIR of modified starch depicts the presence of O-H bonds C=C & C-F bonds.while FTIR Spectra of unmodified starch shows presence of C-Oand C-H bonds.

Fig 2: FTIR modified starch & FTIR unmodified starch

3.4. Water solubility index & water absorption index

Water solubility index of unmodified starch was 8.64 g/ml & 7.52g/ml for modified starch.Water absorption index of unmodified starch was 3.16g/ml & that of modified starch was 4.05 g/ml.

3.5. Swelling power

Swelling power of modified starch was 21.65 g/ml as compared to swelling power of unmodified starch 0.53g/ml.

Table 3: Swelling power of unmodified & modified starch Sample Swelling power (g/ml) UMS 0.53±0.007 MS 21.65±0.671

3.6. Enzyme Hydrolysis

Modified starches were resistant to enzyme hydrolysis.

Table 4: Enzyme hydrolysis of unmodified &modified starch Time Absorbance (540nm) UMS Glucose Concentration UMS Absorbance 540nm MS Glucose Concentration MS 5 min 0.92±0.02 1.01±0.02 0.10±0.01 0.09±0.01

3.7. Acid Hydrolysis

Modified starch was resistant to acid hydrolysis Table 5: Acid hydrolysis of unmodified starch & modified starch Time (min) Absorbance UMS Absorbance MS Control group 1 0.041±0.02 0.050±0.01 Control group 2 0.333±0.01 0.333±0.04

3.8. Prebiotic potential of modified starch

Colonies of pediococcus & bifido bacterium increased in number on increasing modified starch concentration.

Fig 3: Pediococcus & Bifidobacteria strains with 1% & 5 % modified starch cultures

3.9. Proximate Analysis of oatmeal cookies

Nutrient content of all the oatmeal cookies was same with slight variation after the addition of modified starch.

3.9.1. Energy Composition

All oatmeal cookies had somewhat similar energy composition with a slight variation because of the addition of 1 % & 5 % modified starch.

3.9.2. Texture Analysis

All cookies showed somewhat similar textural properties with slight variations.

3.9.3 Sensory evaluation

All cookies were accepted by respondents & showed similar sensory evaluation results with slight variations.

4.1. Discussion

Across the globe, potato is considered the foremost horticultural crop to provide bulk to human diet.Alkali steeping is a method of starch extraction which is relatively simpler.The unmodified starch yield through alkali steeping after ultra sonication method was 49.35 % (w/w).The modified starch or resistant starch yield was 29.95% (w/w).According to a method of Paul Chen starch yield percentage from potato peel was 49%.Water absorption index of unmodified starch was 8.64 g/ml & water absorption index of modified starch was 7.52 g/ml. The water solubility index of unmodified starch was 3.16 g/ml & that of modified starch was 4.05 g/ml. Swelling power of modified starch was 21.6 g/ml as compared to swelling power of 0.53 g/ml corresponding to unmodified starch. Proximate analysis of cookies with the addition of modified starch was also done that depicted a result with slight variations in each sample of oatmeal cookies.Sensory evaluation of oatmeal cookies was done on a 9 point hedonic scale which showed all cookies were generally acceptable with a slight variation.Modified starch was resistant to enzyme & acid hydrolysis & depicted a prebiotic potential in it through Bifidobacterium & Pediococcus bacteria strains.

Fig 5: Standard curve unmodified starch concentration

Conclusion

In conclusion starch can be extracted from potato peel and can be modified to use in a biological application because modified starch isolated from potato peel has a prebiotic effect that induces a variety of benefits for human health. The findings of the study fully support the notion that modified starches extracted from potato peel contain in them prebiotic potential as the Pediococcus and Bifidobacteria colonies multiplied in tenfold within 24 hours of incubation.

Acknowledgements

All glory belongs to Allah the mighty one alone.I deem it a privilege to express my cordial gratitude to my supervisor Dr Syed Farhat Ali for his genuine guidance & Dr Bilal Sadiq for his never ending support.Thanks to Dr Kauser Abdullah Malik & Dr Samina Mehnaz for their encouragement & unwavering appreciation.My sincere thanks to Mr Jibran & Mr Shingraf & all staff of F.C College.I acknowledge with gratitude the genuine care of my family & reassuring behaviour of my peers.