Impact of Blanching Treatments on the Physicochemical Qualities of Kinnow Peel Powder and its Utilization for Cupcake Formulation

Kashagoni Kalyani1, Dashrath Bhati1,*, Harendra2, Deepak Maurya2, Dinesh Baboo Tyagi3
1Department of Horticulture, School of Agriculture, ITM University Gwalior-474 001, Madhya Pradesh, India.
2School of Agricultural Sciences, GD Goenka University, Sohna-122 103, Gurugram, Haryana, India.
3Faculty of Agriculture Sciences, Mandsaur University, Mandsaur-458 001, Madhya Pradesh, India.
Background: This study aims to determine the effects of blanching on the physicochemical characteristics of kinnow peel powder (KPP) and its suitability for cupcake formulation. 

Methods: The kinnow peels (KPs) were divided into five groups according to different blanching times at 95±5°C: 0 minutes (control), 2 minutes (T1), 4 minutes (T2), 6 minutes (T3) and 8 minutes (T4). All the blanched and control KPPs were examined for functional properties and proximate and organoleptic attributes. 

Result: The findings revealed that an increased blanching time affected the functional properties of KPP and varied significantly at a 5% significance level. The titratable acidity was reduced, with T4 exhibiting the lowest value (1.03±0.010). However, with the increased blanching time, the pH, bulk density, water absorption index and oil absorption capacity were also increased and reported as 6.32, 7.05 g/cc, 4.98 gm/gm and 2.04 gm/gm, respectively. The maximum protein content was observed in T4 (7.11 gm/100 gm) and its minimum values were recorded in crude fat (1.07±0.010 gm/100 gm), crude fibre (7.15±0.030 gm/100 gm), total mineral (3.54±0.035 gm/100 gm) and carbohydrates (70.79±0.11 gm/100 gm). An increase in the blanching time positively impacted the organoleptic attributes and reduced the bitter taste of the KPP (T4), boosting the overall acceptability of KPP. Hence, T4 was selected in cupcake formulation at 0% (TCC0), 10% (TCC1), 20% (TCC2), 30% (TCC3) and 40% (TCC4). It was noted that TCC2 might be used for cupcake formulation at the industrial level.
Citrus is one of the most popular fruits worldwide. The genus citrus comprises more than 162 species and belongs to the family Rutaceae (Samson, 1986). It is primarily grown in the USA, Brazil, Mexico, India and Argentina. Among various citrus species, kinnow was created as a hybrid of two citrus cultivars: King (Citrus nobilis) and Willow leaf (Citrus deliciosa). It was introduced in India in 1940 (Mahawar et al., 2019). The production of citrus in India, especially kinnow, has increased with time; presently, the total output for the year 2021–2022 (first advance estimate) of kinnow in India was 6,046 tonnes. Madhya Pradesh (Indian state) is the leading producer of kinnow, with 2,060.55 tonnes, with a share of 32.89% of the total output from India (NHB, 2022).
Kinnow is mainly processed for juice processing; therefore, it produces a yield of 45% for juice and by-products such as peels (27%), rag and pulp residue (26%) and seeds (Mahaot et al., 2016). Overall, kinnow peel (KP) generates approximately 50% of solid waste. The KP contains different bioactive compounds such as carotenoids, flavonoids, phenolic acids, among others (Safdar et al., 2017; Manthey and Grohmann, 2001). Flavonoids are present in higher concentrations in peels than in seeds. It also includes other phytochemicals such as ascorbic acid, hesperidin, naringin, naringenin, narirutin limonin and pectin and other phenolic compounds (Sidhu et al., 2016). Because of these compounds, KP also exhibits antimicrobial activities, making them effective against bacteria and fungi (Ahmad et al., 2006).
KP is structurally subdivided into flavedo and albedo. The flavedo is the peripheral, coloured part rich in essential oils, which causes a burning sensation in the mouth and extreme dryness in the mucous membranes upon contact. The albedo is the inner, spongy and white portion of the peel containing bitter flavanone (Akyildiz and Aðçam, 2014; Berhow et al., 1998). These compounds cause primary and delayed bitterness (Gorinstein et al., 2006) and reduce the product’s acceptability among consumers (Ferreira et al., 2008).
Blanching helps destroy the enzymatic activity in fruits and vegetables. It also alters the organoleptic and nutritional attributes (Ben Zid et al., 2015). Therefore, this study aims to assess the effects of blanching on the physicochemical properties of kinnow peel powder (KPP) and its suitability in cupcake formulation.
Procurement of kinnow and collection of peel
Ripen fruits were purchased from the local market of Gwalior in a single lot. Fruits were washed with lukewarm water followed with tap water to remove wax and all the extraneous material present on the surface of the fruits. All the fruits were wiped out with the help of tissue paper to remove the extra moisture present on the surface. Manual peeling was done to collect the kinnow peels.
Blanching of KP
The KP were divided into five groups according to their times of blanching at 95±5oC: 0 minutes (Control), 2 minutes (T1), 4 minutes (T2), 6 minutes (T3) and 8 minutes (T4) (Fig 1). Sun-drying is one of the oldest methods and zero cost of drying as well as very much feasible to small and marginal farmers residing in Madhya Pradesh. Therefore, all the blanched KP were sundried separately and then powdered.

Fig 1: Processing of kinnow peel for blanching treatment.

Assessment of functional properties of KPP
The pH and titratable acidity of the blanched KPP were analysed by the method proposed by Ranganna (2012).
Bulk density
The bulk density of the samples was calculated by the method of Okaka and Potter (1979). The powdered sample was poured into a dry and clean 25 ml measuring cylinder up to the 10 ml graduation. Continuous tapping was used to pack the powdered particles into the designated volume compactly. More powder was added until the powders reached the 10 ml graduation level. The results were expressed in g/cc.
Water absorption index
The water absorption index of the samples was assessed by the method suggested by Mateos-Aparicio et al., (2010). The KPP (0.5 g) was mixed with 20 ml of distilled water and left at room temperature (25°C) for 24 hours. The centrifugation was conducted for 10 minutes at 4200 rpm. After that, the sediments were collected and weighed. The results were expressed in gm/gm.
Oil-holding capacity
The method described by Zhang et al., (2011) was slightly modified to measure the oil-holding capacity. In total, 0.5 g of sample was combined with 5 ml of sesame oil using a vortex. It was then kept at 4°C for an hour. Next, it was centrifuged for 15 minutes at 4200 rpm. The results were expressed as gm/gm.
Swelling capacity
The approach outlined by Zhang et al., (2011) was used with a few minor modifications to measure the swelling capacity of samples. In a measuring cylinder, 0.4 g of precisely weighed powdered sample was added, followed by 10 ml of water. The mixture was then hydrated for 18 hours at 4°C. Next, the volume fraction and sample volume (ml) were documented.
Evaluation of proximate composition of blanched KPP
Moisture, crude protein, crude fat, crude fibre and total minerals of the samples were determined by the method suggested by AOAC (2005). The carbohydrate content was calculated using the difference (by subtracting the total percentages of moisture, crude protein, crude fibre, crude fat and ash from 100%). The energy content was measured through the physiological fuel value (Mudambi et al., 1989).
Organoleptic evaluation of kinnow peel powder
The blanched powder samples of KPPs were given to a 31-member panel comprising professors, assistant professors and research associates from the Department of Horticulture, ITM University, Gwalior, India, for organoleptic assessment. Organoleptic analysis was conducted to determine the flavour, aroma, texture, feeling in mouth (taste), aftertaste, bitterness and overall acceptability of the powder samples (Larmond, 1970). A single blanched KPP (T4) was selected for cupcake formulation based on the organoleptic evaluation of blanched KPP.
Development and organoleptic evaluation of the developed cupcakes
The selected blanched KPP was incorporated in the amounts of 0% (TCC0), 10% (TCC1), 20% (TCC2), 30% (TCC3) and 40% (TCC4) in the standardised recipe of cupcakes. Organoleptic evaluation of the cupcakes was determined by using a nine-point hedonic rating scale (Larmond, 1970). A 31-member panel, as mentioned above, performed the assessment.
Evaluation of proximate composition of kinnow peel cupcakes
The proximate composition of KP cupcakes was analysed by the method suggested by (AOAC, 2005). The carbohydrate content was calculated using the difference (by subtracting the total percentages of moisture, crude protein, crude fibre, crude fat and ash from 100%). The energy content was analysed by the physiological fuel value (Mudambi et al., 1989).
Statistical analysis
The results obtained during the investigation were statistically analysed using factorial completely randomised design in R software. The results were interpreted through the analysis of variance at a 5% significance level (Gomez and Gomez, 1984).
The effects of blanching on KPP were analysed to determine its functional properties, organoleptic properties and proximate composition. The upcoming subsections discuss these results in detail.
Functional properties
Table 1 presents the results on the functional properties of blanched KPP. The pH and acidity were found to be inversely proportional. This study’s data depict the declining trend in the titratable acidity with respect to the increase in the blanching time, for example, in T4 (1.03± 0.010). The bulk density, water absorption index and oil absorption capacity in T4 were increased with an increase in the duration of blanching and were reported as 7.05±0.070 gm/cc, 4.98±0.050 gm/gm and 2.04±0.020 gm/gm, respectively. However, the swelling capacity was reduced with the increase in the blanching time, except for T3. This outcome may be attributed to experimental errors.

Table 1: Functional properties of blanched KPP.

Mann and Aggarwal (2013) and Ojha and Thapa (2017) on the functional properties of KPP. The hot water blanching led to the swelling of the KPP. Furthermore, it resulted in an increase in the pH and a decrease in the total titratable acidity with respect to an increased blanching time. The KP is subdivided into flavedo and albedo. Blanching causes cell swelling. The heat damages the cell membranes, thus making them permeable (Fellows, 2019).
Proximate composition of blanched KPP
The findings demonstrate significant differences in the proximate composition of blanched KPPs (Table 2). The blanching treatment reduced the relative composition of the blanched KPP. The blanching time was found to be inversely proportional to the crude fat, mineral and fibre contents of the blanched KPP. The highest protein content was observed in T4 (8 minutes of blanching) at 7.11±0.021 gm/100 gm, followed by T3 (6 minutes of blanching) at 6.84±0.062 gm/100 gm. The lowest protein content was observed in T0 (Control) at 6.11±0.040 gm/100 gm. The minimum ash content was recorded in T4 (3.54±0.035 gm/100 gm), followed by T3 (3.75±0.021 gm/100 gm), T2 (3.87±0.087 gm/100 gm) and T1 (4.12±0.031 gm/100 gm).

Table 2: Proximate composition of blanched KPP (gm/100 gm).

This study’s results are consistent with the studies conducted by Bejar et al., (2011), Mann and Aggarwal (2013). The results revealed significant differences in the proximate composition of blanched KPP. The blanching treatment caused a reduction in the proximate composition of the blanched KPP. It is evident from these outcomes that the blanching time is inversely proportional to the crude fat, mineral and fibre contents of the blanched KPP. Fellow (2019) reviewed the blanching treatment and observed similar results for water-soluble components such as minerals, vitamins and other structural elements. This finding is attributed to leaching and thermal destructions. However, Puupponen-Pimia et al., (2003) presented contradictory results on the crude fibre content. Their study was conducted to describe the effects of blanching on 20 common vegetables and found that the fibre content may increase in the blanched vegetables.
Organoleptic evaluation of blanched KPP
Among all the blanching KPPs, the highest aftertaste parameter of KP was recorded in T4 (8 minutes of blanching) with a value of 7.48, followed by T3 (6 minutes of blanching) with a value of 7.23 (Table 3). The minimum value (6.39) of the aftertaste parameter of KP was recorded in T0 (Control). The increase in the blanching time positively improved the acceptability and reduced the bitterness of KPP. Therefore, T4 (8 mins of blanching) KPP was selected for further investigation and development of KP-incorporated cupcakes.

Table 3: Organoleptic evaluation of blanched kinnow peel powder.

Ben Zid et al., (2015) conducted a study on the steam (60 mins at 85°C) and water blanching (10 mins at 95oC) treatment of the citrus peel. They observed that water blanching helps in the swelling of the cells and in reducing the bitterness of the citrus peel. The organoleptic evaluation of the KPP of this study also supports the study of Ben Zid et al., (2015).
The cupcakes were developed by incorporating T4 (8 mins of blanching) KPP in different concentrations of 0% (TCC0), 10% (TCC1), 20% (TCC2), 30% ((TCC3) and 40% (TCC4).
Organoleptic properties of blanched KP cupcakes
Table 4 shows the overall acceptability of KP cupcakes. The maximum acceptability was recorded for TCC0 (8.58±0.24) and the minimum for TCC4 (7.08±0.14). The results revealed that an increase in the concentration of KPP reduced the acceptability of the cupcakes. The study concludes that 20% of KP may be incorporated for developing nutritionally enriched cupcakes with flavour masking. Therefore, cupcake with 20% KP (TCC2) was further analysed for the proximate composition.

Table 4: Organoleptic properties of blanched kinnow peel cupcakes.

Proximate composition of blanched kinnow peel cupcakes
Among all the different concentrations of blanching of KP cupcakes, the highest energy content value of the KP cupcakes was recorded in treatment TCC0 (control) with values of 353.53 Kcal/100 g, followed by TCC1 (10% of KPP) with a value of 351.35 Kcal/100 g (Table 5). The least value of 345.44 Kcal/100 g was recorded for the energy content of the KP cupcake in TCC4 (8 minutes of blanching).

Table 5: Proximate composition of blanched kinnow peel cupcakes (gm/100 gm).

The increased blanched KPP resulted in increased fibre contents and materials, weakening the gluten network. The fibre disorganised the starch-gluten matrix and decreased the gas retention capacity (Aydogdu et al., 2018). It affects the overall acceptability of the cupcakes. Therefore, CCT2 (20% blanched KPP) may be used for cupcake formulation.
The study results evinced that the blanching of KPP for 8 minutes enhances the organoleptic attributes of KPs. This cupcake obtained after blanching for 8 minutes (T4) can be regarded as the best KP cupcake. The cupcakes prepared by incorporating blanched KKP (20%) will help enhance the fibre content in the processed products. The citrus peel contains different antioxidant properties; therefore, the products prepared using blanched KPP would also assist in antioxidant-rich product formulation. However, more research works must be conducted on the loss of antioxidant contents while blanching with respect to time duration.
The authors acknowledge the support and laboratory facilities provided by the ITM University Gwalior, Madhya Pradesh, India.
The authors received no financial support for the research, authorship and/or publication of this article.
Kashagoni Kalyani, Dashrath Bhati and Harendra: Conceptualisation and methodology; Dashrath Bhati: Supervision, writing, reviewing and data analysis; Deepak Maurya and Dinesh Baboo Tyagi: Validation and formal analysis.

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