The Effects of Ripening on the Functional Properties of Plantain and Plantain Based Cake

Abstract

The effects of ripening on the chemical composition and functional properties of plantain at different post harvest stages were studied. The cake baking performance of composite flour made from the blends of the plantain flour and wheat flour at different substitution levels were also evaluated. The result of proximate analysis showed that there were slight increases in moisture content, crude fibre, and ash and fat content as ripening progressed. The carbohydrate was shown to decrease while the protein increased from 2.8% in unripe plantain to 3.5% in firm ripe plantain; it then decreased to 2.6% in softripe plantain. Emulsion capacity, oil and water absorption capacities, viscosity, and swelling capacity were found to be higher in unripe plantain flour than firmripe flour, while whipping capacity of firmripe plantain flour was slightly higher than that of unripe plantain flour. It was also observed that as ripening progressed, the drying rate of the plantain slices decreased. The result of the sensory evaluation of composite flour cake from the plantain showed that the unripe plantain flour produced more acceptable cakes than those made from the firmripe plantain flour at all levels of substitution of the wheat flour. Acceptable cakes could be produced from wheat flour substituted up to 50% with any of the plantain flours.

INTRODUCTION

Plantain, the edible fruit of the genus musa, is one of the major crops of the humid lowland tropical areas, whose production in Nigeria has gained considerable importance in recent years. The crop develops with firm starchy fruits which ripen usually after harvest to soft sweet fruits of high sugar and low acid content of characteristic flavour and texture.[1,2] Ogazi[3] reported that over 80% the crop is harvested during the period of September to February, and that there is much wastage at this time as some of the products do not store for a long period. This results in seasonal availability and limitations on the use by urban population. Plantain is nutritionally a low protein food material but relatively high in carbohydrate, minerals, and vitamins.[4,5,6] The unripe fruit is used as a starchy staple food in humid forest zones. Usually after boiling, it is eaten with red palm oil or pounded and eaten with vegetable stew and meat. Ripe plantains are cut into slices and fried into doodoo (Nigeria'sYouruba food) and eaten with tomato stew.[7,8] Lawker[9] reported that ripe plantains and bananas with their high sugar and low starch contents can be used in infant food formulation as well as food for invalids who may have problems with carbohydrates digestion.

Ndubuizu[10] defined ripening as a process composed of complex interrelated but separate physiological events resulting from biochemical and biophysical changes occurring at cellular, subcellular, and molecular levels. Ripening in plantain occurs once the fruit matures. During ripening, chlorophyll is degraded by enzyme chlorophyllase to a colourless product, thus, exposing the carotenoids.[11] Changes in colour and texture of plantain fruit during ripening is associated with changes in proximate composition and functional properties. Kassim[12] and Ogazi[13] in their independent research have shown that the moisture, sugar, protein, lipid, and fibre contents of unripe plantain increase during ripening while the carbohydrate content decreases.

Functional property has also been defined by Matil[14] as those characteristics that govern the behaviour of nutrients in food during processing, storage, and preparation as they affect food quality and acceptability. Some of the important functional properties that influence the utility of most starchy staples, such as plantain, include the drying characteristics, water absorption capacity, emulsion capacity, oil absorption capacity, whipability, foam stability, viscosity, and swelling capacity. In every plantain market, bunches of plantain are sold, which are at various stages of maturation with little or no scientific method to assist the customer or determine what he or she is buying.[7] There have been no exploitative studies on the processing and utilization of plantain at different stages of ripening. The present work is, therefore, an attempt to investigate the changes in chemical composition and functional properties of plantain flour due to ripening as well as to ascertain the best post harvest stage for the plantain flour processing and utilization in cake production.

MATERIALS AND METHODS

The plantains used for this experiment were harvested from the plantain orchard of the university of Nigeria Nsukka. The species was false horn plantain, and the ripening was carried out at room temperature. The drying characteristics of the fresh plantain slices were determined using unripe, firmripe, and softripe plantain slices and done in a hot air oven drier at 60-70°C (Gallenkamp model). Samples of plantain fresh fingers were randomly collected from different heads of the bunch and peeled. They were then cut into 0.5cm thick slices and dried (weight measurements were taken at 20 min intervals). The proximate composition of the samples was determined according to AOAC[15] methods. The water absorption capacity was evaluated according to the Benchat[16] method. In this method, 2g of the sample was mixed with 20 ml distilled water using ultra Turax T mixer. The mixture was allowed to stand at room temperature for 30 min. The supernatant was decanted, and the volume was used to calculate the water absorption capacity. Method of Lin et al.[17] was used to assess the swelling capacity. In this method, 1g of the sample was suspended in 10 ml distilled water, vortexed, and heated for 1 hr in a boiling water bath with stirring and shaking. The heated suspensions were centrifuged at 2000g for 20 min, and volumes of supernatants and sediments were read off. Increases in volume of the sediments at this time were also measured. Oil absorption capacity was determined by the Benchart method.[16] Two grams of sample were mixed with 20ml groundnut oil for 5 min at room temperature using ultra- Turax T 25 mixer for 1min. The mixture was centrifuged at 5000 × 6 r.p.m. The supernatant was decanted and used to calculate the amount of oil absorbed. In the determination of emulsion capacity, the method described by Lin et al.[17] was used. Thus, 1.8g of sample was dispersed in 25ml distilled water and 25ml vegetable oil (groundnut oil) added. The 50ml mixture was emulsified at high speed using ultra-Turax T 25 mixer for 1min. The emulsions were filled into centrifuge tubes and centrifuged for 5 min. at 1300 × 6 r.p.m. Percentage emulsion was then expressed as

where χ is height of emulsified layer and y is height of whole solution in the centrifuge tube. Whipability and foam stability were determined by the method of Coffman and Gracia.[18] In this method, 2g of sample was weighed into 60ml distilled water in a 100ml cylinder. The solid material was dispersed with spatula, and the suspension was whipped for 5 mins using ultra-Turax T 25 mixture at a high speed. Volumes before and after whipping were noted, and the volume increase due to whipping was calculated. The volume of foam in the standing cylinder was also recorded for foam stability studies at 1, 5, 10, 20, 30, 60, 90, 120 and 180 min after whipping.

The viscosity was evaluated using the method of Sathe et al.[19] Concentrations of samples at 2%, 4%, 6%, 8%, and 10% were prepared by dispersing the appropriate samples in distilled water and mechanically stirring for 2 hrs at room temperature. An Oswald type of viscometer was used to measure viscosity at the different concentrations. The relative viscosity was calculated as the ratio of viscosity of the concentrated sample to the viscosity of water. In the plantain flour processing, the modified method of Ogazi[13] was employed. The plantain fingers were peeled and cut into thin slices of 0.05cm thickness. The slices were dried at 60-70°C and then milled using a hammer mill. The flour produced was sieved using 425-300 micro metre mesh size sieve to get fine flour of desired particle size.

Cake baking was carried out with a composite flour blend of the plantain flour and wheat flour at different substitution levels. Typical baking recipe used had the following ingredients: flour (200g), sugar (150g), margarine (180), baking powder (1.5g), egg (260g), and salt (45g). Baking was done according to Ihekereonye and Ngoddy.[20] The sensory evaluation was conducted on the baked cakes using a 10: man panel of judges. A 7-point hedonic scale was used to assess the crust colour, crumb colour, texture, air cells, crumb homogeneity, sponginess, flavour, and general acceptability. In the hedonic scale, 7 represents extreme desirability while 1 represents extreme undesirability for both flavour and general acceptability. In crust colour, 7 represents extremely brown and 1 extremely yellow; for crumb colour, 7 means extremely yellow and 1 extremely creamy; for texture, 7 is extremely soft and 1 is extremely hard; for sponginess, 7 is extremely spongy, 1 is extremely compact; for air cell, 7 is extremely small, 1 is extremely large; for crumb homogeneity, 7 is extremely homogenous, 1 extremely heterogeneous. The result of the evaluation was analyzed using analysis of variance (ANOVA) and mean separation carried out using Duncan multiple Range Test (Coputer M.Start C Programme was used) according to Wahua.[21]

RESULTS AND DISCUSSION

The result of the drying characteristics showed that the drying rate decreased as the stages of ripening increases. Drying at 60–70ºC for two hours reduced the weight of the unripe plantain slices from 200g to 15g, which is about 92.5% moisture removal, while the firm ripe and softripe slices had 45g and 65g, which are about 76.5% and 67.0% moisture loss, respectively (Table 1). The softripe plantain was still so soggy after drying that it could not possibly be milled into flour. The difficulty in drying and milling of the more ripened plantains could be attributed to the increased sugar content at the ripened stage, which has more hydrophilic affinity than the starches in the unripe plantain.

Table 1 Changes of weight of plantain slices with time during drying

Time (min)	Unripe plantain (g)	Firm ripe plantain (g)	Softripe Plantain (g)
0	200^a	200^a	200^a
20	100^a	140^a	160^a
40	80^b	120^ab	145^a
60	70^b	100^ab	120^a
80	40^b	80^ab	100^a
100	30^b	60^ab	80^a
120	15^b	45^a	65^a
Mean values with different superscript on the same row are significantly different (p< 0.05).

The result of the proximate analysis (Table 2) showed that moisture content, fat, crude fibre, and ash increased with ripening while the carbohydrate decreased. The decrease in moisture content is consistent with the report of Awan and Ndubuizu,[11] who observed that the moisture content of plantain increased from 49.4–57.5 from the time of harvest to 14 days of storage. This is also in agreement with the findings of Kassim[12] and Ogazi.[13] The protein content of the unripe plantain increased from 2.8% to 2.6% when softriped, which also agrees with the earlier report of Landele et al.[5] Giami and Alu[2] reported an increase of 32.3% and 50.3% protein contents of fully ripe and overripe plantain pulp, respectively. Aseidu[22] observed an increase of 24.1% in crude protein content of plantain pulp during ripening and attributed such increase to the conversion of enzymes and/or protein synthesis. Palmer and McGlasson[23] in their own report emphasized that protein synthesis is required for the ripening of fruits. These biochemical changes, Ndubuizu[10] also attributed to some biological and chemical reactions taking place in the plantain during ripening.

Table 2 Proximate composition of plantain at three stages of maturity

Constituent	Unripe Plantain	Firm Ripe Plantain	Softripe Plantain
Moisture content (%)	61.62^a	62.50^a	36.96^a
Fat content (%)	1.40^b	1.75^b	2.52^a
Crude fibre (%)	0.65^a	0.75^a	0.90^a
Crude protein (%)	2.80^b	3.50^a	2.60^b
Ash (%)	1.00^c	2.00^b	2.50^a
Carbohydrate (%)	33.93^a	29.94^b	27.52^b
Mean values with different superscript on the same row are significantly different (p< 0.05).

In the analysis of the functional behaviours of the flours, only the flours of the unripe and firmripe plantain were used since sound flours with necessary analytical quality could not be obtained from the softripe plantain. The unripe plantain flour demonstrated a higher water absorption capacity and swelling capacity than the firmripe plantain (Table 3). These higher values are associated with higher starch content in the unripe plantain flour whose complex molecule will demand more water during hydrolysis than sugar molecules.[20] The high water absorption and swelling capacities have both economic and culinary advantage. Therefore, the unripe plantain flour will seem better in the production of pastry and baking foods. Emulsion capacity and oil absorption capacity of the unripe plantain are higher than in the firmripe plantain (Table 3.) High emulsion capacity and oil absorption are very beneficial in baking products requiring emulsion and creaming properties, such as the cake production. Although the whipping capacity of the firmripe plantain was higher (Table 3.), the foam stability of the unripe plantain flour was higher (Table 4). Whipping capacity is dependent on the protein. The firmripe plantain with higher protein content demonstrated higher whipping capacity. In culinary processing, foam stability is very essential, and since the unripe plantain flour maintained reasonable foam stability throughout the 180 minutes after whipping, it should be very useful in such processing. Viscosity is very much dependent on the starch component. As expected, unripe plantain flour showed higher viscosity per unit rise in concentration (Table 5).

Table 3 Functional properties of unripe and firmripe plantain flours

Functional property	Unripe plantain	Firm ripe plantain
WATER ABSORPTION CAPACITY (ML/G)	2.50^a	2.00^a
SWELLING CAPACITY	3.00^a	2.40^a
OIL ABSORPTION CAPACITY (ML/G)	5.33^a	4.00^b
Emulsion capacity (%)	47^a	45^b
Whipping capacity (%)	9.35^a	8.08^b
Mean values with different superscript on the same row are significantly different (p< 0.05).

Table 4 Foam stability of unripe and firmripe plantain flours

	Volume of foam (ml)
	Time (min)
Sample	0	1	5	10	20	30	60	90	120	180
Unripe plantain	73	72	72	72	70	72	72	71	71	71
Firmripe plantain	73	74	70	69	69	69	68	68	68	69

Table 5 Relative viscosity of unripe and firmripe plantain flours at different concentrations

Concentration (%)	Unripe plantain	Firm ripe plantain
2	1.04	1.00
4	1.05	1.02
6	1.10	1.07
8	1.22	1.11
10	1.27	1.15

The result of sensory evaluation (Table 6) showed that in all respects, sample E, the 100% wheat flour cake, distinguished itself as the best. In terms of general acceptability and flavour, sample E was closely followed by sample D, containing 25% unripe plantain flour with 75% wheat. The same trend was noted in crumb homogeneity, air cells, sponginess, texture, crumb colour, and crust colour. Following next in quality in all these characteristics were samples B, the 50% unripe flour with 50% wheat, then sample G, containing 50% firmripe with 50% wheat flour. The poorly performed samples were shown by samples made from 75% blend of either the unripe or firmripe plantain flours with 25% wheat and the 100% cakes made from either of the plantain flours. In general, however, the quality of the cake decreased as the substitution level of the wheat flour with any of the plantain flour increased. The 50% substitution of the wheat flour still gave acceptable cakes; beyond this level, however, desirability reduced drastically. The result generally confirms the superiority of flours from the unripe plantain over that from the firmripe plantain in baking cakes.

Table 6 Sensory evaluation of unripe and firmripe plantain/wheat composite flour cakes

Sample	Crust color	Crumbcolor	Texture	Sponginess	Air cells	Crumb homogeneity	Flavor	General acceptability
100% unripe	6.1^a	2.8^d	2.6^c	3.3^b	6.0^a	5.2^ab	4.9^c	4.9^d
50% unripe with 50% wheat	5.0^b	3.2^d	4.6^b	4.5^ab	5.6^ab	5.6^a	5.5^bc	5.6^c
75% unripe with 25%wheat	5.9^a	3.3^d	5.3^ab	4.4^ab	4.5^b	4.7^b	5.2^c	5.1^d
25% unripe with 75% wheat	4.3^bc	3.5^cd	5.7^a	4.9^ab	4.0^b	5.1^ab	6.1^b	6.0^b
100% wheat	4.1^c	4.2^c	5.2^ab	5.2^a	3.0^b	5.5^ab	6.5^a	6.6^a
75% firmripe with 25% weat	6.0^a	6.4^a	5.3^ab	4.9^ab	4.8^b	5.0^ab	5.4^bc	5.1^d
50% firmripe with 50% wheat	4.8^bc	5.5^b	4.8^b	4.6^ab	4.2^b	4.9^ab	5.8^b	5.5^c
25% firmripe with 75% wheat	5.0^c	5.1^b	4.1^b	4.6^ab	4.3^b	5.0^ab	5.9^ab	5.8^bc
100% firmripe	5.8^a	6.7^a	6.0^a	3.3^b	4.4^b	4.5^c	4.7^c	4.1^c
Mean values with different superscript on the same column are significantly different (p< 0.05).

CONCLUSIONS

Ripening in plantain initiated some changes, which influenced the functional behaviour of the plantain flours. These changes, occurring at different post harvest stages, ultimately underscore the utility and suitability of plantain in different food preparations. Unripe plantain has been established to produce a better bakery product (cake) than the firmripe plantain.