Introduction

Persea americana Mill. Lauraceae is a fruit indigenous to Central America and Mexico and is now cultivated in tropical and subtropical locations worldwide (Cowan and Wolstenholme 2016). The common name for this fruit is “avocado,” which is also known as “alligator pear” and “butter pear” (Duarte et al. 2016). More than 500 avocado varieties are available all around the world. However, most of them are not commercially feasible owing to various factors, including development time, protein and fat content, tolerance issues, and damages during shipping (Hurtado-Fernández et al. 2018). The three ecological races are Mexican, Guatemalan and West Indian. Each race has distinct leaves, fruits and blooming features and some types have exterior skins with brown-black hints. The fruit may weigh up to 500 g and the ovoid-shaped seed size becomes larger as the fruit develops (Shikwambana 2016).

Avocados are popular because of their rich, creamy, velvety texture and a mild taste. The high-fat content gives a rapid feeling of “fullness,” which reduces overeating and acts as a weight-loss tool. The monounsaturated fatty acids (oleic and palmitoleic acids) speed up the metabolic rate compared to saturated fatty acids. When the fruit ripens, the palmitic acid concentration falls and oleic acid content increases (Villa-Rodríguez et al. 2011), making oleic acid (45%) the primary fatty acid in avocado (Nnaji and Okereke 2016). The fruit contains 9% of carbohydrates, of which 7% constitute the fiber part, making it a low carbo plant food that favors the diabetic group. The pulp has a more significant proportion of insoluble (70%) and soluble fibers (30%) (Nnaji and Okereke 2016). The spongy mass of fibre enables consumers to fulfil their appetites and also assists in food passage through the alimentary canal by supporting the muscular activity of the colon, lowering the danger or incidence of constipation (Princewill-Ogbonna et al. 2019).

Avocado’s global output will be 8.06 million tons in 2020. Mexico is the world’s largest producer, contributing 45% of total world production. The avocado market is expected to reach 23 million dollars by the end of 2027. The USA is the number one importer, while Mexico, Peru, Colombia and Chile are the top-ranking exporter countries (Nations 2021). The comment, “avocados are a challenging crop to obtain maximum quality”, is an often-overlooked fact. Nowadays, customers have more access from harvesting to distribution operations. Post-harvest temperature management significantly impacts preserving quality and educating the farmers about it would reduce rotting. This issue may be handled by processing the versatile fruit into semi-processed intermediate goods, like pulp, which is still nutritious. Just like in any other sector, these stored commodities will then have the opportunity to be transformed into valuable things when processors or customers require them.

Avocado pulp is extremely perishable due to the presence of enzymes that promote quick darkening when exposed to oxygen. These browning enzymes are denatured by a combination of time and temperature during heat treatment (Moon et al. 2020). The ideal pre-treatment parameters for the production of Hass avocado pulp using high-caliber raw material have been determined (Salvador-Reyes and Paucar-Menacho 2019). However, these estimates are of little use for the West Indian race since it has a different fruit size and diameter; therefore, their heating time is different. Looking at the significance of the fruit and the knowledge gap about this fruit, the present study attempts to evaluate the influence of pre-treatment on the chemical composition of West Indian race avocado pulp.

Methods and materials

Preparation of samples

Mature avocado fruits cv. Pollock was procured from the local growers adjoining the Kodaikkanal region, Tamilnadu, during 2020–2021. The mature fruit was ripened within 8 days of harvesting.

Process of elaboration

Mature, ripe avocados were chosen, washed and then subjected to various pre-treatments as shown in Fig. 1.

Fig. 1
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Elaboration process of avocado pulp preparation

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The pre-treatments were carried out for 3 min. To prevent heat burn on avocado, it is immediately submerged in cold water after pre-treatment. Each pre-treatment was performed in triplicates. The pulp collected was stored in PET containers at 4 °C and − 20 °C. The analysis was performed on alternate months for 6 months.

Avocado pulp’s quality characteristics

During storage, variations in the quality characteristics of experiments were observed. The pulp was evaluated for physicochemical parameters (carbohydrates, proteins, fat, titratable acidity and browning) (AOAC 2004) and sensory characteristics (color and appearance, taste, texture and overall acceptability). A preference analysis test was conducted with 20 customers aged 19–28, utilizing a 9-point hedonic scale. The overall acceptability of prepared products was based on the mean score of all sensory characteristics. These data were then subjected to multivariant analysis of variance (MANOVA) at p ≤ 0.05 using SPSS version 16, where the chemical constituents are considered dependent and treatments as the independent variable (Table 1).

Table 1 The pre-treatments on avocado fruit
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Results and discussion

Avocado pulp output was 73.76% on average. The remainders, such as seeds and peel, accounted for 15% and 10.52%, respectively Avocado pulp yield varies from 52.9 and 81.3% of the total fruit weight (Tango et al. 2004). Kruger et al. (1995) observed Hass avocado pulp yield to 71.37%. While Nnaji and Okereke (2016) stated that the pulp makes up 65% of the fruit, the seed is 20% and the skin is 15%. Krumreich et al. (2018) noticed the pulp yield as 71.89%, whereas Ejiofor et al. (2018) evaluated the pulp yield of Hass avocados as 71.37%. Salazar-López et al. (2020) noticed the pulp yield as 73%. Galvao et al. (2014) evaluated three different variants: Fortuna, Collinson and Barker, whose pulp was found to be 75%, 69.5% and 73%, respectively. A study on avocado pulp yields from several cultivars revealed that Fuerte and Hass types had the best performance, with 69.8%, since they have a lighter and smaller seed than other varieties (Jimenez et al. 2021). Salvador-Reyes and Paucar-Menacho (2019) estimated the average flesh output for Hass avocados to be 79.23%. West Indian race avocados had a larger seed and peel weight than other varieties, the fruit weight was also higher, resulting in a higher pulp yield (Table 2).

Table 2 Yield efficiency of the West Indian race avocado
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The avocado pulp had a high moisture level of 67%. These data imply that West Indian race avocado fruit should be adequately handled to retain quality and increased shelf life. The present study’s findings agreed with those of (da Vinha et al. 2013), who revealed that the peel, pulp, and seed of Hass avocado fruit exhibited a high moisture content (> 50%). There was no significant difference in the moisture percentage among the treatments; however, when the treated samples were stored for the shelf-life study and were thawed for additional research, their moisture percentage increased. The moisture content increased greater in refrigerated samples than in frozen ones (Table 3).

Table 3 Effect of pre-treatments on moisture content in avocado pulp and its stability during storage
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Table 4 indicates the change in carbohydrate content during refrigerated and deep freezer storage. Though untreated samples of West Indian race avocado had a carbohydrate level of 10.75%, after six months at 4 °C, it substantially decreased to 6.32%. The treatment T5 followed a similar pattern, but the T2 retained carbohydrates at 8.87% after 6 months. However, after 6 months in a deep freezer, the avocado pulp preserved the same percentage of carbohydrates in T2 (10.14%). The decrease in the carbohydrates may result from the breakdown of the polysaccharides into simpler components (Nnaji and Okereke 2016).

Table 4 Effect of pre-treatments on carbohydrates in avocado pulp and its stability during storage
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The fat content of the avocado from the West Indian race is 13.63%, which dropped to 11.82% by the sixth month. There was a significant difference in the fat percentage between the treatments during storage (Table 5). For all pre-treatments, the fat content decreased when kept at 4 °C. While the fat in the avocado pulp in the deep freezer was also reduced to 12% except for T2 treatment, which was maintained at 13%. The hydrolysis of triacyl glycerides results in the accumulation of free fatty acids, which can be explained by the activity of lipase enzymes and phospholipase. Similar studies were reported by Lurie et al. (1987), Kolodyaznaya et al. (2019) and Flores et al. (2017).

Table 5 Effect of pre-treatments on fat content in avocado pulp and its stability during storage
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Concerning the protein content, the untreated pulp had a protein level of 2.57% (Table 6). The protein decreased significantly during refrigerated storage and was cut down to 1.41%. All of the pre-treatments in the refrigerator followed the same pattern. However, for storage at – 20 °C except for T2, all pre-treatments show a slight decline. The Maillard reaction strongly depends on the storage conditions such as temperature, water activity, time and compositions. Within these factors, temperature and carbohydrate content have the most significant impact on the extent of the Maillard reaction Garcia-Amezquita et al. (2014), Gullón et al. (2016), Norwood et al. (2017). When stored, several amino acids in protein powders can undergo deamidation, transamidification, dehydration, β-elimination reaction, and isomerization (Geiger and Clarke 1987; Gerrard 2002). These reactions will also result in changes in protein content. The results were in agreement with other studies reported by Isah (2017), Patras et al. (2011), Bekele et al. (2020) and Aimi Azira et al. (2021).

Table 6 Effect of pre-treatments on protein content in avocado pulp and its stability during storage
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The acidity of the pre-treated samples ranged from 0.30 to 0.38% on day zero (Table 7). The change in acidity was more significant for refrigerated storage than deep freezer. The acidity of the T2 treatment was lower when compared to other treatments. It is reported that acidity increases as the storage time increase. The increase is due to the conversion of complex carbohydrates into simpler ones and later, a rise in acidity evidenced its conversion. The other reason Calvo-Garrido et al. (2008) suggested is the release of acids in the vacuoles. Comparable studies were carried out in avocado puree by Jacobo-Velázquez and Hernández-Brenes (2012), Parasnis et al. (2000) in papaya chutney, Daisy et al. (2004), Ghimire (2022) in dehydrated aonla, Sharma et al. (2006) in dehydrated apple rings, Sra et al. (2014) in dehydrated carrot slices.

Table 7 Effect of pre-treatments on acidity in avocado pulp and its stability during storage
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After quick pulping, the pulp displayed greater L* and b* values in T1 samples. The ‘L’ value in refrigerated storage decreased with time, reaching 38 in the sixth month, whereas the a-value varied from -9.93 on the first day to + 8.44 on the sixth (Table 8). While among the treatments, the T5 had a better L value (59.83) in the sixth month than all other pre-treatments. The main finding was that the browning of the avocado pulp was only evident on the crust, while the pulp retained its color in the inner portions of the container (Fig. 2). The intensity of browning depends on the factors combined to preserve the purees, the packaging material and its atmosphere. Soliva et al. (2000) and Salvador-Reyes and Paucar-Menacho (2019) reported similar studies in this aspect. On the other hand, the samples in the freezer showed relatively minor color changes.

Table 8 Effect of pre-treatments on avocado pulp color and its storage stability at 4 °C
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Fig. 2
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Changes in pulp color on zero-day and at 6 months

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The sensory evaluation of the pulp was performed only on the first day of pre-treatments. The data (Table 9) revealed that treatment T5 showed the highest score, while treatment T3 reported the minimum score. On statistical evaluation by analysis of variance (ANOVA), T5 (2% Brine and 2% citric acid) had no significant difference from the control (T1), while all other treatments had a significant effect on their organoleptic characteristics. The results imply that the T5 treatment is the most acceptable with reference since it is similar to the untreated avocado pulp. This indicates that consumers prefer avocado pulp with intense color. There were no variations in preference concerning taste and texture. Latapi and Barrett (2006) reported that brine and citric acid treatment would stabilize the color and texture and prevent the leaching out of essential constituents than other pre-treatments.

Table 9 Changes in the organoleptic quality (9 Point scale) of pretreated avocado pulp
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The findings of the purchase intention survey reveal that customers favored the ‘T5' and control samples. In comparison, a significant proportion of them said that they would not purchase avocado pulp from treatment ‘T3’. The current study established that avocados grown in Kodaikanal, Tamilnadu state, had a different composition than those grown in other geographical places. This variance might be explained by the temperature and soil conditions in which it flourishes. According to the study, avocado fruit has a greater concentration of most chemical components. Additionally, it would be a beneficial dietary supplement.

Conclusion

The current study’s findings led us to infer that West Indian race avocados are feasible for pulp production due to their high pulp output of 73.76%. Additionally, the pre-treatments accompanied with 2% brine and 2% citric acid for 3 min preserved the green color and brightness of the pulp, preventing enzymatic browning even after 6 months under refrigerator conditions. The ‘T2’ and ‘T3’ pre-treatments added the product’s acid stability, extending its shelf life more than the other treatments. Thus, the ideal duration and pre-treatment temperature for preparing West Indian race avocado pulp was 70 °C for 3 min since this treatment retard enzymatic browning, thus preserving the pulp’s organoleptic features (taste, smell, and color). The chemical contents of the pulp at – 20 °C did not change significantly between the control and pre-treated avocado pulp; however, the browning effect had a significant difference. This study revealed that it is practically viable to conserve fruit for 6 months when handled appropriately. As a result, customers will have access to avocados throughout the year, which will aid in developing high-value goods, resulting in increased revenue for growers and businesses.