Analysis of alcoholic fermentation of pulp and residues from pineapple processing

Abstract

The purpose of this paper was to analyze the utilization of pulp and residues from pineapple processing as substrates for alcoholic fermentation. The fruits were cleaned, ground, and hydrolyzed with pectinase, cellulase, hemicellulase, and amylase. Pineapple pulp and whole fruit were analyzed to determine the amounts of amide, hemicellulose, total reducing sugars, °Brix, pectin, cellulose, and lignin present. Fermentation experiments were conducted with 0, 100, 200, and 300 g/kg of peel. Wines were analyzed for total or volatile acidity, total reducing sugars, and ethanol. The assays with the highest fermentation kinetic parameters were analyzed to determine the secondary compounds in the wine. The results showed that the enzymatic hydrolysis decreased the polysaccharide amount and increased reducing sugars and soluble solids, thereby improving the fermentation process, mainly in integral samples. In pineapple fermentation, 100 g/kg of peel addition did not influence the kinetic parameters and secondary compounds analyzed from the pineapple wines were within the legal limits.

El propósito del presente estudio consistió en analizar el uso de la pulpa y de los residuales descartados durante el procesado de piña, como posibles sustratos para la fermentación de alcohol. Los frutos fueron lavados, molidos e hidrolizados con pectinasa, celulasa, hemicelulasa y amilasa. Se analizaron la pulpa de la piña y la fruta entera para determinar su contenido de amida, de hemicelulasa, de azúcares reductores totales, de °Brix, de pectina, de celulosa y de lignina. Las fermentaciones se realizaron con 0, 100, 200 y 300 g/kg de cáscara. Asimismo, se examinaron los vinos con el fin de determinar la cantidad de acidez total o volátil, de azúcares reductores totales y de etanol. Los ensayos con los parámetros de fermentación cinética más altos fueron analizados con el objetivo de determinar los compuestos secundarios presentes en el vino, constatándose que la hidrólisis enzimática redujo la cantidad de polisacáridos y elevó los niveles de concentración de azúcares reductores y los sólidos solubles, lo cual mejoró el proceso de fermentación, principalmente en las muestras integrales. Se concluye que si se agrega 100 g/kg de cáscara en la fermentación de piña, no se alteran los parámetros cinéticos y, además, los compuestos secundarios analizados en los vinos de piña se mantienen dentro de los límites legales.

Keywords:

• tropical fruit
• residues
• enzymatic hydrolysis
• alcoholic fermentation

Palabras claves:

• fruta tropical
• residuos
• hidrolisis enzimática
• fermentación alcohólica

Introduction

Fruit is an important crop of Brazil; however, there is a high amount of waste material. This waste includes season surplus, especially since it is a degradable raw material. Therefore, large amounts of bad fruits are daily discarded because of defects in the peels, sizes, color, and consistency, among other factors. Fruit processing generates a large amount of residues such as peels, wastes, and seeds, among other parts originated from each production step, varying according to the specific product. There is thus the need to develop new processes to minimize losses and increase the small cropper’s income. Finding viable alternative to agro-industrial residues is fundamental today. One of the alternatives is fermentation to produce vinegars and liquors.

Food industries produce waste that could be reused by man and benefit the environment. They are materials that can be a source of proteins, enzymes, essential oils, and other reusable products. The utilization of residues from fruit processing in the alcoholic fermentation step can generate special, more valuable products, besides avoiding waste. Generally, sweet raw materials are good fermentation substrates. Bortolini, Sant’anna, and Torres (2001) have assessed acetic fermentation in kiwi juices. Nogueira, Santos, Paganini, and Wosiacki (2005) have analyzed alcoholic fermentation in apple-waste extract. Asquieri, Silva, and Cândido (2009) have produced jabuticaba spirit with peel and waste from fermented jabuticaba manufacture. Silva et al. (2009) have produced banana spirit with banana peel and banana pulp and tested its physicochemical and sensorial quality. Further research needs to be developed using other fruits, such as pineapple, processed worldwide.

Products obtained from the fermentation of fruit residues and fruit exceedings are an alternative for fruit croppers to minimize vintage losses, although more research is necessary considering the fact that this is a new issue for study. The production of fruit wines is already well-established, and many tropical fruits are used in the process, such as orange (Corazza, Rodrigues, & Nozaki, 2001), sugar–apple, mangaba, ciriguela (Muniz, Borges, Abreu, Nassu, & Freitas, 2002), acerola (Santos, Almeida, Toledo, Santana, & Souza, 2005), and jaca (Assis Neto, Cruz, Braga, & Souza, 2010). This study aims to quantify the secondary compounds derivable from alcoholic beverages made from different fruits. The analysis of these compounds has the purpose of checking whether the characteristics of the product stay within legal limits (Garruti, Franco, Silva, Janzantti, & Alves, 2003).

This work aimed to study the reuse of residues from pineapple processing in alcoholic fermentation. The main analysis persists in evaluating the effect of enzymatic hydrolysis in raw material treatment with percent-determination of residuals added to the must, which would not interfere with alcoholic fermentation’s kinetic parameters besides determining the concentration of secondary compounds in the alcoholic beverages obtained.

Materials and methods

Source of pineapples

The pineapples used in this study were of the variety ‘pérola’ (Ananas comosus (L.) merril) in the last stage of maturation obtained from local markets in Belo Horizonte, Minas Gerais (Brazil).

Sanitization and raw-material processing

The pineapples were washed in tap water, left 15 min in chloride solution, and rinsed with distilled water. The pineapple-pulp sample (PP) was obtained from peeled fruits ground in an electric mixer, whereas the integral-pineapple sample (IP) was obtained after grinding unpeeled fruits in a mixer.

Enzymatic hydrolysis

Samples of PP and IP were enzymatically hydrolyzed, producing hydrolyzed pineapple pulp (HPP) and hydrolyzed integral pineapple (HIP). Commercial enzymes (Pectinex Ultra-SP enzyme, Celluclast R, Spring alfa, and Summer Xylan) were used as shown in Table 1. Later, enzymatic deactivation was carried out for 5 min in a water bath at 90°C.

Table 1. Pulp- and integral-pineapple enzymatic hydrolysis conditions.

Tabla 1. Condiciones de la hidrólisis enzimática de pulpa de piña e piña integral.

Enzymes	Pectinase	Cellulase	Hemicellulase	Amylase
Commercial name	Pectinex Ultra SP	Celluclast^R	Summer Xylan	Spring Alfa
Concentration (mg/kg)	250	1000	60	600
Time (min)	78	30	30	30
Temperature (°C)	35	35	35	55
References	Alvarenga, Geocze, Silva, and Oliveira (2011)	Yuliarti, Matia-Merino, Goh, Mawson, and Brennan (2011)	Granotec do Brasil (2009)	Granotec do Brasil (2009)

Thermo-gravimetric and physico-chemical analyses

The samples were analyzed through thermo-gravimetry. TG/DTG curves were obtained by means of a TGA-50H scale (Shimadzu). Between 11.0 and 17.0 mg sample were used in an aluminum crucible (Al₂O₃) under nitrogen dynamic atmosphere (50 mL/min flow) and 10°C/min heating ratio, up to 750°C.

Pineapple pulp and integral pineapple, having undergone or not enzymatic hydrolysis, were analyzed for amide amount (IAL, 1985), total reducing sugars (Miller, 1959), pH (AOAC, 1992), total soluble solids (AOAC, 1992), pulp amount (Koch, 1971), hemicelluloses, pectin, lignin, and cellulose (Schieber, Fügel, Henke, & Carle, 2005).

Experimental design

A completely randomized design was used with three replications.

Alcoholic fermentation

Alcoholic-fermentation tests were performed in flasks Erlenmeyers with 100 mL pineapple pulp, whether peeled or not (musts), which were incubated in a heating chamber at 30°C for 24 h. A bakery jammed-ferment (Itaiquara) constituted by Saccharomyces cerevisae at the concentration of 20 g/L was used as inoculate. Musts were fermented with 100, 200, and 300 g/kg of peel with and without enzymatic hydrolysis. All assays were performed in triplicate with 120 g/L total reducing sugars.

Musts samples were collected both at time zero and by the end of fermentation, and centrifuged for 5 min at 7462 G in a Janetski centrifuge; supernatant was analyzed for acidity, total reducing sugars (TRS), and ethanol amount.

Acidity was determined through titrimetry with 0.025 M sodium hydroxide solution, according to ABNT (1997). As for the determination of initial total reducing sugars (must), as well as for the final TRS (wine), the DNS method (3,5 dinitrosalicilic acid), by Miller (1959), was used.

Ethanol concentration was spectrographically determined through the modified potassium dichromate method (Salik & Povoh, 1993). In that reaction, in acid solution, ethanol is oxidated to acetic acid, and the solution turns green and greener proportionally to ethanol concentration in the sample. Yellow bichromate ion is reduced to green chromous ion absorbing at 600 nm. Absorption is proportional both to the concentration of chromous ion formed and to oxidated ethanol (Crowell, 1961).

Kinetic fermentation-parameters’ calculation

The calculated parameters were productivity (g/L∙h), ethanol production (%), and yeast efficiency (%). Productivity expresses the ethanol mass produced (g) over volume (L) of the fermenting mean by time unit (h), allowing for the determination of transformation speed from sugar to ethanol. Ethanol production was determined in relation to the theoretical ethanol amount expected for the must after its sugar amount determination. The expected sugar amount was calculated considering that 1g total reducing sugars produce 0.511 g ethanol (Cardoso, 2006; Hashizume, 2001). The efficiency of the conversion substrate (total reducing sugars) to ethanol by yeast, as percentage, expresses the amount of the ethanol produced relative to the theoretical quantity expected based on the sugar content of the must.

The pineapples wines, with 100 g/kg of added peel, and without peel-addition, underwent enzymatic hydrolysis and were analyzed to determine acidity, total soluble solids, pH, alcoholic amount, and secondary compounds.

The total soluble solids amount was measured through a 0–32° Brix hand-refractometer (Instrutemp, São Paulo, Brazil) (IAL, 1985). Total acidity was determined through titrimetry with sodium hydroxide, according to ABNT (1997). pH was determined through a digital potentiometer (IAL, 1985). The real alcoholic amount was determined through densitometry (ABNT, 1997).

Total esters (ethyl-acetate, ethyl-lactate), aldehydes (acetaldehyde), total superior alcohols (n-propanol, isobuthanol, isoamilics), o-methanol, furfural, 1-buthanol, and 2-buthanol through chromatographic analyses (GC/FID), were determined, following the Vinegars and Liquors Operational Handbook (Brasil, 2005). The analyses were performed in gas-chromatographer, FID detection system, mark Intercom, model Generation 8000, carbowax column 0.53 mm X 30 m X 1.00 uM, with nitrogen flux 30 mL min^–1, hydrogen flux 30 mL min^–1, and air flux 300 mL min⁻¹. The injector temperature was 140°C and the detector temperature was set to 180°C. The column temperature was held for 3 min at 35°C after injection, and then programmed at 5°C min⁻¹ from 35 to 80°C, and at 6,07°C.min⁻¹ from 80°C until 165°C, with a total run time of 30 min. The sample was previously distilled. Quantification was carried out by integration of the peak areas using the external standardization method. The standard curve of each compound was prepared by plotting the concentration against the area. 1-Pentanol was used as internal standard.

The analyses were performed in triplicate. The kinetic parameters’ results were compared in the ANOVA/Tukey test with 5% probability margin and the results for acidity, total soluble solids amount, ART, and pH, as well as the secondary compounds, were analyzed using Student’s t-test in the SISVAR software developed by Ferreira (2011).

Results and Discussion

IP presented higher hemicellulose and lignin + cellulose amount than PP. HIP presented lower lignin + cellulose, amide, and pectin amount than non-hydrolyzed integral pineapple due to the action of the enzymes used. Non-hydrolyzed samples presented a lower amount of total soluble solids (°Brix) than the hydrolyzed samples, demonstrating °Brix increase whenever the raw material undergoes enzymatic hydrolysis (Table 2).

Table 2. Characterization of the main polysaccharides from pineapple samples undergoing different treatments.

Tabla 2. Caracterización de los principales polisacáridos a partir de muestras de piña de diferentes tratamientos.

Parameters/Treatments	Integral, non-hydrolyzed	Integral, hydrolyzed	Non-hydrolyzed pulp	Hydrolyzed pulp
Hemicellulose (g/kg)	10.2 ± 2.6^a	7.2 ± 2.0^ab	5.7 ± 0.6^b	4.7 ± 1.2^b
Lignin + Cellulose (g/kg)	19.0 ± 4.0^a	7.3 ± 2.1^b	8.2 ± 1.3^b	6.7 ± 0.6^b
Amide (g/kg)	2.2 ± 0.3^a	0.9 ± 0.2^b	1.7 ± 0.8^ab	1.1 ± 0.4^ab
Pectin (g/kg)	1.8 ± 0.3^a	0.4 ± 0.1^b	1.6 ± 0.1^a	0.2 ± 0.1^b
°Brix	10.0 ± 0.2^d	11.7 ± 0.4^c	12.8 ± 0.3^b	14.6 ± 0.1^a
Total reducing sugar (g/L)	94.0 ± 1.7^b	114.0 ± 4.4^ab	108.3 ± 18.2^ab	126.7 ± 13.5^a

Note: *Means with different letters in the same line differ significantly in Tukey test (p < 0.05).

*promedios seguidos por la misma letra en la misma linea no difieren entre sí en prueba de Tukey (p < 0.05).

These gravimetric results indicate that both hydrolyzed and non-hydrolyzed samples undergo complete thermo-decomposition at 700°C. In the HPP curve, the hydrolysis effect was not detected, unlike HIPs, probably because of the integral sample’s higher polysaccharides concentration.

According to Aggarwal and Dollimore (1998), more structural alterations occur during enzymatic hydrolysis, exposing a larger zone to heat action and consequently making thermo-degradation easier, thereby explaining the more accentuated thermo-degradation in HIP, as shown in Figures 1 and 2.

Figure 1. Mass loss from pineapple pulp (PP) and hydrolyzed pineapple pulp (HPP).

Figura 1. Pérdida de masa de la pulpa de piña (PP) y pulpa de piña hidrolizada (PPH).

Figure 2. Mass loss from integral pineapple (IP) and hydrolyzed integral pineapple (HIP).

Figura 2. Pérdida de masa de la piña integral (PI) y piña integral hidrolizada (PIH).

Supernatant’s volumes obtained from HPP and HIP were greater than the ones obtained from PP treatments. Pulp amounts (supernatant’s volumes) from HPP and HIP exceeded those obtained from the same samples but not hydrolyzed, as shown in Table 3, demonstrating that hydrolysis decreases mean viscosity, allowing better productivity in centrifugation. This result indicates the necessity of hydrolyzing the raw material before fermentation, on behalf mainly of proceedings to be used in filtration and centrifugation.

Table 3. Supernatant’s volumes from the different treatments assessed.

Tabla 3. Volúmenes de sobrenadante de los diferentes tratamientos evaluados.

Treatment	Pulp amount (%)
Pulp (PP)	65.47 ± 0.26^b
Hydrolyzed pulp (HPP)	71.26 ± 0.12^a
Integral (IP)	50.99 ± 0.31^c
Integral, hydrolyzed (HIP)	61.01 ± 0.10^b

Note: *Means with different letters in the same column differ significantly in Tukey test (p < 0.05).

*promedios seguidos por la misma letra en la misma columna no difieren entre sí en prueba de Tukey (p < 0.05).

Initial must’s acidity values were 0.52 g acetic acid per 100 mL pineapple-pulp wine with 100 g/kg of peel pineapple pulp. As for fermentation with 200 and 300 g/kg of peel, acidity values were 5.5 and 5.4 g/L, respectively. Final acidity varied from 5.8 to 6.2 g/L between the treatments. Must with the largest peel amount presented slightly higher acidity values.

Total reducing sugars’ final amount varied between 6.0 and 11.3 g/L. For the wine obtained without peel, whether hydrolyzed or not, total soluble solids’ final amounts were lower than those for wines with peels addition, showing that peel makes total consummation of those solids harder during fermentation. For non-hydrolyzed must, total reducing sugars were 6.0, 6.8, 9.4, and 11.3 g/L, with 0, 100, 200, and 300 g/kg of peel, respectively. For hydrolyzed must, the concentrations were 6.7, 7.2, 8.1, and 7.1 g/L with 0, 100, 200, and 300 g/kg of peel, respectively. Musts with the largest amount of pineapple peel produced less ethanol and obtained more total reducing sugars at the end of fermentation, reflecting the yeast efficiency. Table 4 shows that fermentations using the largest amounts of peel presented the lowest ethanol production.

Table 4. Means from kinetic parameters for pineapple fermentation.

Tabla 4. Medios de parámetros cinéticos para la fermentación de piña.

Pineapple	Production (Ethanol yield) (%)	Yeast efficiency (%)	Productivity (g/Lh)
Non-hydrolyzed pulp without peel	74.73 ± 1.85^bc	79.57 ± 2.11^b	1.64 ± 0.10^d
Hydrolyzed pulp without peel	84.25 ± 0.41^a	90.44 ± 0.47^a	1.95 ± 0.01^a
Non-hydrolyzed pulp + 100 g/kg of peel	74.17 ± 0.85^b	79.46 ± 0.98^b	1.74 ± 0.01^b
Hydrolyzed pulp + 100 g/kg of peel	82.89 ± 2.63^a	89.86 ± 3.04^a	1.94 ± 0.01^a
Non-hydrolyzed pulp + 200 g/kg of peel	59.18 ± 0.98^e	65.10 ± 1.09^cd	1.39 ± 0.01^f
Hydrolyzed pulp + 200 g/kg of peel	71.91 ± 0.50^c	79.15 ± 0.60^c	1.67 ± 0.03^c
Non-hydrolyzed pulp + 300 g/kg of peel	55.54 ± 0.15^f	59.94 ± 0.18^d	1.29 ± 0.01^g
Hydrolyzed pulp + 300 g/kg of peel	63.87 ± 0.17^d	68.95 ± 0.20^c	1.48 ± 0.02^e

Note: *Means with different letters in the same column differ significantly in Tukey test (p < 0.05).

*Medias con letras diferentes en la misma columna difieren significativamente en la prueba de Tukey (p < 0.05).

Fermentation’s kinetic parameters of hydrolyzed pulp, both with 100 g/kg of peel and without peel, did not differ significantly between each other, showing that 100 g/kg of pineapple-peel addition does not decrease ethanol production, not even yeast efficiency. In all fermentations, the values of kinetic parameters after hydrolysis exceeded those found for the same parameters whenever the must did not undergo hydrolysis, except for productivity after fermentation with 200 g/kg of peel.

It was observed that fermentative parameters for ethanol production and efficiency had similar results as those from sugarcane spirits (Oliveira, Rosa, Morgano, & Serra, 2004). Briones, Hernández, and Úbeda (2002) produced melon spirits using as raw materials the whole melon, pulp, and seed, with a production lower than the production found in this work. Bortolini et al. (2001) found ethanol production values between 38.65% and 47.23%, in a study on kiwi juice’s alcoholic fermentation.

The ethanol yield using commercial yeast was 94.06% in a study on banana juice’s alcoholic fermentation (Alvarenga et al., 2011).

The results of the analyses of acidity, total soluble solids amount, pH, and alcoholic amount are shown in Table 5.

Table 5. Acidity amount, °Brix, pH, and alcoholic amount of the pineapple wines.

Tabla 5. Tasas de la acidez, ° Brix, pH y tasa alcohólica de los fermentados de piña.

Parameters	Pineapple wine with 100 g/kg of peel added	Pineapple wine without peel addition
Acidity
INITIAL	0.46% (V/V) a	0.41% (V/V) a
FINAL	0.55 % (V/V) a	0.52 % (V/V) a
°Brix
FINAL	3.8° Brix a	3.5° Brix a
pH
INITIAL	3.7 a	3.85 a
FINAL	3.35 a	3.40 a
Alcoholic amount
FINAL	6.8° GL a	5.9° GL b

Note: *Averages followed by the same letter in the same line do not differ between each other in t-test.

*promedios seguidos por la misma letra en la misma línea no difieren entre sí en test t (p < 0.05).

The initial acidity averages of the wines analyzed did not differ between one another, not even the acidity analyzed at the end of the process. These values stay above the acidity found for the cajá wine (2.0 g/L), assessed by Dias, Schwan, and Lima (2003) and below the results found by Corazza et al. (2001) for the acidity of the orange wine (8.1 g/L).

Regarding the fermented beverages of fruits, the total acidity amount must range between 3.3 and 7.8 g/L (Rizzon, Zanuz, & Manfredini, 1994). Comparing total acidity at the beginning and at the end of the process, it was observed that the parameter did not duplicate its value. According to Almeida, Silva, Conrado, Mota, and Freire (2011), this fact indicates that there was no excessive production of organic acids; in other words, there was no bacterial contamination.

Soluble solids at the end of fermentation did not differ significantly from wines with and without pineapple peel (Table 1). Non-fermentable substances dissolved in the must can explain this result at the end of fermentation. According to Corazza et al. (2001), the soluble solids are not necessarily constituted by the total amount of sugars. Similar results were found by Muniz et al. (2002) after assessing the fermentation of ata, ciriguela, and mangaba.

According to Table 5, pH at the beginning and at the end of fermentation did not differ significantly (p > 0.05) for the musts assessed. The fruit wine’s pH usually oscillates between 3.0 and 4.0 (Hashizume, 2001), as found in this work. According to Hashizume (2001), the pH value at the end of the pineapple wine fermentation without the peel is considered ideal to lessen bacterial contamination problems. Corazza et al. (2001) obtained a final pH of 3.3 in orange wine. Jabuticaba pulp wines reached a final pH of 3.3 (Asquieri, Candido, Damiani, & Assis, 2004). As for the mangaba, ata, and ciriguela wine, Muniz et al. (2002) obtained pH values of 3.21, 4.12, and 3.06 respectively. Lopes and Silva (2006) obtained for fig-of-India a final pH of 3.5.

Pineapple wine added with 100 g/kg of peel presented a higher alcoholic amount. Both pineapple wines presented results within the Brazilian legal limits for liquors (Brasil, 1997). Muniz et al. (2002) found 8.4, 9.8, and 10.1°GL for the ata, mangaba, and ciriguela wine, respectively. Arruda, Casimiro, Garruti, and Abreu (2003), in a paper on banana wine processing, obtained alcoholic graduation going from 8.9 to 9.1% v/v. Reddy and Reddy (2009) obtained similar results with mango wine.

The esters, aldehyde, superior alcohols, n-butylic alcohol, sec-butylic alcohol, methanol, and furfural amount are described in Table 6.

Table 6. Secondary compounds from pineapple wines.

Tabla 6. Compuestos secundarios de fermentados de piña.

Parameters (mg/L)		Pineapple wine
		With 100 g/kg of peel	Without peel
Esters
	Ethyl acetate	60.0 ± 2.6 a	26.6 ± 0.5 b
	Ethyl lactate	0.0	0.0
Aldehyde
	Acetic acid	30.6 ± 2.5 a	31 ± 4.0 a
Superior alcohols
	n-propylic	46,1 ± 0.9 b	61.3 ± 0.8 a
	isobutylic	58.1 ± 0.9 b	62.3 ± 0.6 a
	isoamylic	193.0 ± 0.9 a	169.9 ± 1.0 b
n-butylic alcohol		0.0	0.0
Sec-butylic alcohol		0.0	0.0
Methylic alcohol		65.2 ± 1.5 b	74.2 ± 2.9 a
Furfural		0.0	0.0

Note: *Averages followed by the same letter in the same line do not differ between each other in t-test.

*promedios seguidos por la misma letra en la misma línea no difieren entre sí en test t (p < 0.05).

Ethyl acetate concentration was higher in the pineapple wine with 100 g/kg of peel (Table 6), and the results found in this study were below those found in the fermented beverage of cajá (Dias et al., 2003). The high ethyl acetate amount provides an acetic taste to the wines, spoiling their quality (Rizzon et al., 1994). Ethyl acetate represents around 80% of the wines’ volatile esters (Almeida et al., 2011). Ethyl acetate concentrations between 50 and 80 mg/L contribute to the product’s aroma (Garruti et al., 2003). Considering the referred range suggested by Garruti et al. (2003), only the alcoholic pineapple beverage with peel in the fermentation has the ideal ethyl concentration to contribute to the product’s aroma. Oliveira, Cardello, Jeronimo, Souza, and Serra (2005) state that ethyl acetate concentrations below 200 mg/L provide the wine with an agreeable odor.

The acetic aldehyde amount in the wines did not differ significantly between one another (p > 0.05). Concentrations below those of the present study were found in the mandacaru-fruit bre (154.33 mg/L) assessed by Almeida et al. (2011), and in the caju wine (Torres Neto, Silva, Silva, Swarnakar, & Silva, 2006), with a concentration of 690 mg/L. Acetaldehyde, formed along the alcoholic fermentation, is a product of the primary fermentation metabolism, unchained after the amino acids in the fermentative mean and after the ethanol oxidation. Garruti et al. (2003) state that the high amount of acetaldehyde is responsible for the oxidation odor.

In pineapple wines with and without 100 g/kg of peel, the superior alcohols concentrations were below 400 mg/L, thus benefiting the product’s aroma. Concentrations above 400 mg/L contribute negatively to the wine quality, since they produce disagreeable odors (Garruti et al., 2003). According to the results presented in Table 6, pineapple wine without peel addition presented higher n-propilic and isobutylic amount, and a lower concentration of isoamilic alcohol. Superior alcohol concentrations in the pineapple wine were lower than the concentrations found for mandacaru wine (1905.63 mg/L) (Almeida et al., 2011). Superior alcohols are formed along the fermentation, out of amino acids such as leucin, isoleucin, and valin, present in the musts or resulting from the hydrolysis of yeast cells’ proteins (Garruti et al., 2003). The pineapple wines analyzed in this study presented lower isoamilic alcohol concentration compared with the cajá wine (Dias et al., 2003).

The pineapple wine without peel presented a higher methanol amount (Table 6). Normally, the methanol amounts found in fruit wines are higher in the wines from musts with higher pectin amount, since methanol originates from pectin degradation (Cardoso, 2006). In the case of pineapple, the pectin amount from integral pineapple (with peel) was statistically equal to the pulp pectin amount (Table 2). Therefore, methanol amount was not an issue whenever the peel was used in fermentation. Methanol concentrations were 356.77 mg/L in the mandacaru wine analyzed by Almeida et al. (2011), 100 mg/L in the cashew wine (Torres Neto et al., 2006), and 140.5 mg/L in the grape wine (Manfroi, Miele, Rizzon, & Barradas, 2006).

Methanol is one of the most important components in wine, but its production is not desirable because of its toxicity (Torres Neto et al., 2006). Methanol is toxic to humans, severely affecting the respiratory system and may lead to blindness and death (Cardoso, 2006). In case its production occurs, it must not exceed the limit of 350 mg/L wine or 500 mg methanol/100 mL anhydric alcohol (Salton, Daudt, & Rizzon, 2000).

Conclusions

Enzymatic hydrolysis decreased polysaccharide amount and increased reducing sugars and wine’s soluble solids, thereby improving the fermentation process, mainly in integral samples. In pineapple fermentation, 100 g/kg of peel addition did not influence ethanol production and yeast’s efficiency, which indicates the possibility of using pineapple processing residues without quality losses along the alcoholic fermentation.

All the secondary compounds analyzed from the pineapple wine were within the legal limits. The 100 g/kg of peel added to the wine did not interfere negatively in the physico-chemical quality of the fermented product.

Therefore, pineapple peel can be used both by small croppers and by big processing industries to obtain distillate, vinegar, and ethanol.

Acknowledgment

The authors thank FAPEMIG for the financial support.