Food Chemistry 129 (2011) 312–318

Contents lists available at ScienceDirect

Food Chemistry

journal homepage: www.elsevier.com/locate/foodchem

Comparing physicochemical properties of pulp and peel flours prepared from green and ripe fruits ⇑ Abbas F.M. Alkarkhi a, Saifullah bin Ramli b, Yeoh Shin Yong b, Azhar Mat Easa b, a School of Industrial Technology, Environmental Technology Division, Universiti Sains Malaysia, 11800 Penang, Malaysia b School of Industrial Technology, Food Technology Division, Universiti Sains Malaysia, 11800 Penang, Malaysia article info abstract

Article history: Banana pulp and peel flour prepared from green and ripe were assessed for physico- Received 13 October 2008 chemical properties such as pH, total soluble solids (TSS), water holding capacity (WHC) and oil holding Received in revised form 22 February 2011 capacity (OHC) at 40, 60 and 80 °C, colour values L⁄, a⁄ and b⁄, back extrusion force (BEF) and viscosity. Accepted 22 April 2011 Data obtained were analysed by MANOVA, discriminant analysis and cluster analysis. All statistical anal- Available online 4 May 2011 yses showed that physicochemical properties of flour prepared from pulp and peel, and green and ripe banana were different from each other. TSS, WHC40, WHC60 and BEF can be used to discriminate Keywords: between peel and pulp flour, whilst TSS and viscosity can be used to discriminate between flour prepared Cavendish banana from green and ripe banana. Physicochemical properties Banana pulp flour Ó 2011 Elsevier Ltd. All rights reserved. Banana peel flour MANOVA Cluster analysis Discriminant analysis

1. Introduction such as cakes (Yomeni, Njoukam, & Tchango Tchango, 2004) and extruded products (Gamlath, 2008). Being able to differentiate be- Banana is one of the most consumed fruits in tropical and sub- tween banana flour prepared from different stages of ripeness tropical regions. New economical strategy to increase utilisation of could help food processors to control the quality of food incorpo- banana includes the production of banana flour when the fruit is rated with banana flour. unripe, and to incorporate the flour into various innovative prod- As the fruits of the banana trees are consumed at green, average ucts such as slowly digestible cookies (Aparicio-Saguilan et al., ripe and ripe stages (Emaga, Andrianaivo, Wathelet, Tchango, & 2007), high-fibre bread (Juarez-Garcia, Agama-Acevedo, Sayago- Paquot, 2007), the amount of fruit waste from the peels is expected Ayerdi, Rodriguez-Ambriz, & Bello-Perez, 2006) and edible films to increase with the development of processing industries that (Rungsinee & Natcharee, 2007). The clear advantage presented by utilise the green and ripe banana. Like its pulp flour counterpart, green banana flour includes a high total (73.4%), resistant banana peel flour can potentially offer new products with stand- starch (17.5%) and dietary fibre content (14.5%) (Juarez-Garcia ardised compositions for various industrial and domestic uses et al., 2006). Due to the high content of these functional ingredi- (Emaga et al., 2007). The peel of banana that represents about ents, regular consumption of green banana flour can be expected 40% of the total weight of fresh banana (Tchobanoglous, Theisen, to confer beneficial health benefits for humans (Rodriguez-Ambriz, & Vigil, 1993) has been underutilised. Various studies have been Islas-Hernández, Agama-Acevedo, Tovar, & Bello-Pérez, 2008). On conducted to investigate banana peel, and this include the produc- the other hand, ripe banana flour that is less known banana prod- tion of banana peel flour (Ranzani, Sturion, & Bicudo, 1996), the uct, may offer high sugar content to dishes requiring sweetness. effects of ripeness stage on the dietary fibre components and pec- Other than health and sensory reasons, the stages of ripeness are tin of banana peels (Emaga, Robert, Ronkart, Wathelet, & Paquot, also important for technical aspect of processing. Banana pulp flour 2008) and the chemical composition of banana peel, as influenced prepared using fruits at different stages of ripening has been by the maturation stage and varieties of banana (Emaga et al., shown to behave differently during manufacture of food products 2007). The potential applications of banana pulp and peel flour depend on their chemical composition (Emaga et al., 2007; Rodriguez- ⇑ Corresponding author. Tel.: +60 4 6533888x2222; fax: +60 4 6573678. Ambriz et al., 2008), as well as physicochemical and functional E-mail address: [email protected] (A.M. Easa). properties. However, once the fruit is processed into flour, identifi-

0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.04.060 A.F.M. Alkarkhi et al. / Food Chemistry 129 (2011) 312–318 313 cation of the parts and stages of ripeness of banana used for flour Viscosity was determined as described by Fagbemi (1999). Flour preparation becomes a challenge. As far as we know, no study was dispersed in water at 8% (w/v) concentration using a magnetic has been conducted to compare physicochemical properties of ba- stirrer (1000 rpm) and heated from 30 to 95 °C in a shaking water- nana flour prepared from pulp or peel of green and ripe banana. bath (memmert, Gmbh-Germany) and kept at this temperature for One study that compared the antioxidant compounds in banana 20 min. The slurry obtained was stirred constantly and cooled at peel and pulp extracts found that the content of antioxidant com- room temperature. The viscosity was measured using a Vibro pounds was higher in the peel than in the pulp (Someya, Yoshiki, & Viscometer (SV-10, A & D Japan). Okubo, 2002) implying a potentially higher value of the peel in terms of antioxidant content. Perhaps in the future it may be pos- 2.3. Water- (WHC) and oil-holding capacity (OHC) sible for technologist to mix and match the pulp and peel flour in order to achieve technofunctional properties without sacrificing Twenty-five millilitres of distilled water or commercial olive oil the aesthetic values of their products. This development can spur were added to 1 g of dry sample, stirred and incubated at 40, 60 or the utilisation of banana peel as innovative ingredients in various 80 °C for 1 h. Tubes were centrifuged at 3000g for 20 min, the food and nutraceutical products thus increases the possibility of supernatant was decanted, and the tubes were allowed to drain banana peel in addition to banana pulp to be processed into flour. for 10 min at a 45° angle. The residue was weighed and WHC The physicochemical properties of the flour are expected to vary and OHC calculated as g water or oil per g dry sample, respectively with stage of ripeness as it is known that the composition of (Rodriguez-Ambriz et al., 2008). banana changes dramatically during ripening. It seems worthwhile to study the physicochemical data of banana flour and devise 2.4. Colour methods to discriminate banana pulp and peel flour based on its physicochemical data. Statistical techniques that can be applied The instrumental measurement of flour colour was carried out to perform this task include MANOVA, cluster analysis and with a Colorimeter Minolta CM-3500d (Minolta, Spectrophotome- discriminant analysis (Markus, Elena, Jacinto, & Carlos, 2002; ter, USA) and the results were expressed in accordance with the Ricardo, Pablo, Elena, Jacinto, & Carlos, 2003; Suárez, Rodrl´guez, CIELAB system with reference to illuminant D65 and a visual angle & Romero, 2007). Therefore the objective of this study was (i) to of 10°. The measurements were performed through a 6.4-mm- compare selected physicochemical properties of pulp and peel diameter diaphragm with an optical glass, placing the flour directly flour prepared from green and ripe Cavendish banana, (ii) to use ⁄ ⁄ on the glass. The parameters determined were L (L = 0 [black] and the data to discriminate between the flours, and (iii) to single out ⁄ ⁄ ⁄ ⁄ ⁄ L = 100 [white]), a (a = greenness and +a = redness) and b most appropriate physicochemical methods that differentiate the ⁄ ⁄ (b = blueness and +b = yellowness). flours.

2.5. Back extrusion force of slurry 2. Material and methods A TA-XTplus Texture Analyser (Stable Micro Systems, Godal- ming, UK) was used to evaluate the texture of the flour slurry 2.1. Preparation of banana peel flour (8% w/v). Back ward extrusion tests were conducted with the disc diameter 45 mm, setting the probe travel distance at 30 mm. Both Cavendish ( acuminate L., cv cavendshii) banana, was tests were performed with a test speed of 2 mm/s, a trigger force of purchased from 12 markets around Penang, Malaysia. A total of 5 g, and force in compression mode. Force–time curves were 222–302 green (stage 1 of ripening: all green) and ripe (stage 6 recorded at a crosshead speed of 5 mm/s and recording speed of ripening: yellow with green tip) banana of each stage of ripeness was 5 mm/s to enable evaluation of back extrusion force (BEF) of were obtained from each market. The fruits were washed and the slurry. separated into pulp and peel. The pulps were cut into transverse slices of about 2 mm thickness. To reduce enzymic browning, pulp slices and peels were then dipped in 0.5% (w/v) citric acid solution 2.6. Statistical analysis for 10 min, drained and dried in oven (AFOS Mini Kiln, at 60 °C overnight). The dried pulp slices and peels were ground in a Retsch 2.6.1. Multivariate analysis of variance (MANOVA) Mill Laboratory (Retsch AS200) to pass through 60 and 40 mesh Multivariate analysis of variance is used where several screen to obtain banana pulp and peel flour, respectively. The yield dependent variables (p) are measured on each sampling unit of flour was calculated by dividing the amount of flour produced by instead of one variable. The objective of MANOVA is to com- the amount of fresh banana used, and the results were converted to pare the mean vectors of k groups for significant difference. g/kg (g of flour/kg of banana). Four types of flour produced were Equality of the mean vectors implies that the k means are ripe Cavendish pulp (R-pulp), ripe Cavendish peel (R-peel), green equal for each variable, and if two means differ for just one Cavendish pulp (G-pulp) and green Cavendish peel (G-peel). All variable then we conclude that the mean vectors of the k flours were stored in airtight plastic packs in cold storage groups are different. (15 ± 2 °C) for further analyses. 2.6.2. Discriminant analysis Discriminant analysis is a multivariate technique used for two 2.2. pH, TSS and viscosity purposes, the first purpose is description of group separation in which linear functions of the several variables (discriminant The pH of the flour was measured using a Coming pH metre, functions (DFs)) are used to describe or elucidate the differences model 10. Flour suspension (8% (w/v)) was stirred for 5 min, between two or more groups and identifying the relative contribu- allowed to stand for 30 min, filtered and the pH of filtrate mea- tion of all variable to separation of the groups. Second aspect is sured (Suntharalingam & Ravindran, 1993). Total soluble solids prediction or allocation of observations to group in which linear (TSS) in the same flour slurries were measured using an Atago or quadratic functions of the variable (classification functions refractometer (Atago PAL-1, Co. Ltd., Tokyo, Japan) (Salvador, Sanz, (CFs)) are used to assign an observation to one of the groups (Alvin, & Fiszman, 2007). 2002; Richard & Dean, 2002). 314 A.F.M. Alkarkhi et al. / Food Chemistry 129 (2011) 312–318

2.6.3. Cluster analysis In principle, this could cause less sweetness to be perceived in Cluster analysis (CA) is a multivariate technique, whose primary R-peel flour which in turn could influence consumer acceptance. purpose is to classify the objects of the system into categories or This suggestion however, needs further testing. Three types of clusters based on their similarities, and the objective is to find an soluble sugars, i.e. sucrose, glucose and fructose that have been optimal grouping for which the observations or objects within each detected in banana peel (Emaga et al., 2007) may represent the cluster are similar, but the clusters are dissimilar to each other. TSS of peel flour. Hierarchical clustering is the most common approach in which The mean L⁄ value ranged between 37.6 and 74.2. This indicates clusters are formed sequentially. The most similar objects are first a substantial colour difference existed between the pulp and peel grouped, and these initial groups are merged according to their flour. From visual observation this difference was obvious, i.e. the similarities. Eventually as the similarity decreases all subgroups peel flour was a lot darker than the pulp. Major change in colour are fused into a single cluster. CA was applied to heavy metals in took place during drying of the peel that yielded dark brown sediment data using a single linkage method. In the single linkage powder, particularly in the ripe samples. As banana peel contains method, the distances or similarities between two clusters A and B glucose, fructose and protein (Emaga et al., 2007), an extend of is defined as the minimum distance between a point in A and a the Maillard reaction could had occurred, while certain enzymes point in B: such as polyphenol oxidase may be present in banana peel that could contribute a certain degree of enzymatic browning (Thipay- DðA; BÞ¼minfdðyi; yjÞ for yi in A and yj in Bgð1Þ arat, 2007). This later explanation seems acceptable since the enzymatic browning of banana is well known problem. where dðy ; y Þ is the Euclidean distance in (1). i j During ripening of banana, the flesh colour changes from the At each step the distance is found for every pair of clusters and typical ‘‘opaque white’’ of a product with a high starch content to the two clusters with smallest distance (largest similarity) are a ‘‘very soft yellow’’ as the yellowing of the skin intensifies (Salva- merged. After two clusters are merged the procedure is repeated dor et al., 2007). In fresh banana, the colour changes of peel during for the next step: the distances between all pairs of clusters are cal- storage as a result of ripening has been observed as a loss of green- culated again, and the pair with minimum distance is merged into ness, and increase in reddish and yellowness tones (Salvador et al., a single cluster. The result of a hierarchical clustering procedure 2007) which correspond to increase in the a⁄ and b⁄ values (Chen & can be displayed graphically using a tree diagram, also known as Ramaswamy, 2002) that took place as a result of the breakdown of a dendrogram, which shows all the steps in the hierarchical proce- the chlorophyll in the peel. a⁄ value of the ripe flour was marginally dure (Alvin, 2002; Richard & Dean, 2002). higher than the green, meanwhile b⁄ value of the ripe flour was lower than the green that does not reflect the actual colour charac- 3. Result and discussion teristics of green and ripe banana pulp and peel. Inconsistency in b⁄ value might have been attributed to the excessive browning occur- 3.1. General descriptive statistics ring in the peel during drying, and to some extend the presence of dark spots scattering about the flour and interfere with colour The average length and diameter of Cavendish banana used for analyses. No study could be found on the effect of drying on the study were 18.0 and 6.0 cm, respectively, and the average banana peel, but quality of banana paste as influenced by vacuum weight per fruit was 174 g. Banana peel flour produced was brown- dehydration has been studied by Thipayarat (2007). It was found ish in colour and green pulp flour was creamy pale-yellow in that banana paste dehydrated with vacuum dehydration had colour, whilst ripe pulp flour was light brown in colour. All flour darker colour (lower L value) and more intense yellow colour had visible dark spots scattering about the flour samples, and (higher b value) that was hypothesised to be due to condensation presented banana flavour. The average yield of G-peel, R-peel, and to moisture loss, enzymatic and non-enzymatic browning G-pulp and R-pulp flours were 38.5, 48.6, 159.6 and 118.5 g/kg of (Thipayarat, 2007). fresh banana fruit, respectively. It is evident that pulp yielded more Mean WHC of all flour samples increased with temperature, and flour than the peel, and green pulp yielded the highest amount of ranged between 1.4 and 8.2 g/g dry sample. These values are lower flour compared to others. than those reported in mango dietary fibre (12 and 15 g water/g Table 1 summarises descriptive statistics including the mean, dry sample) and mango peel dietary fibre (11 g/g) (Larrauri, Ruper- standard deviation, maximum and minimum values for all physi- ez, Borroto, & Saura-Calixto, 1996), but were comparable with cochemical properties of flour. The spread around the mean value fibre-rich unripe banana flour (2.5 g/g) (Rodriguez-Ambriz et al., (Standard deviation (Std)) was small and random in all samples, 2008). The mean WHC at all temperatures tested were the highest indicating consistency of samples. The mean pH of flour ranged in R-peel flour (6.1–8.2 g/g dry sample), and was the lowest in between 4.80 to 5.47 and R-peel flour showed the highest pH R-pulp flour (1.4–4.7 g/g dry sample). WHC could be related to whilst G-peel flour showed the lowest. the physical state of starch (Waliszewski, Aparicio, Bello, & Mon- The mean TSS ranged between 1.22 to 4.26 °Brix with the order; roy, 2003), dietary fibre and protein in the flour. According to R-pulp > R-peel > G-peel > G-pulp. TSS indicates soluble solid con- Rodriguez-Ambriz et al. (2008) amylose has the capacity to effec- tent of flour, and high TSS has been associated with high sucrose tively bind water molecules, yielding a higher WHC. However since content in banana pulp (Bugaud, Chillet, Beaute, & Dubois, 2006). starch was low in ripe banana peel (Emaga et al., 2007), the high It has been reported that the average starch content drops from WHC noted in R-peel could be attributed to the dietary fibres 70% to 80% in the pre-climacteric period to less than 1% at the and protein. The increase in WHC at 80 °C in all flour samples end of the climacteric period, while sugars, mainly sucrose, was due partly to protein denaturation, solution properties of accumulate to more than 10% of the fresh weight of the fruit dietary fibre such as hemicelluloses and pectin polysaccharides (Zhang, Whistler, BeMiller, & Hamaker, 2005). The lower TSS of (Zhang et al., 2005) and to a smaller extend to the gelatinisation green banana flour is acceptable since it is known that amylase, of starch in the flour that absorbs water into starch granules with glycosidase, phosphorylase, sucrose synthase and invertase can concomitant swelling (Rodriguez-Ambriz et al., 2008). act in the degradation of starch and the formation and accumula- Another functional property of banana flour is oil holding tion of soluble sugars (Emaga et al., 2007; Terra, Garcia, & Lajolo, capacity (OHC). In general the mean OHC of almost all samples 1983). Since TSS of R-pulp was higher than R-peel, it can be increased with temperature, and ranged between 0.50 and concluded that R-pulp had higher sugar content than R-peel flour. 1.30 g/g dry sample. These values are lower than that reported in A.F.M. Alkarkhi et al. / Food Chemistry 129 (2011) 312–318 315

Table 1 Descriptive statistics for selected physicochemical properties of banana flour.

Parameter Green (G-peel) Ripe (R-peel) Min Max Meanc Stdd Min Max Meanc Std (a) Cavendish peel flour pH 4.30 5.33 4.80 0.42 4.86 5.69 5.47 0.24 TSS (°Brix) 1.53 1.90 1.73 0.12 3.20 3.63 3.46 0.14 L⁄ value 34.83 48.73 40.88 4.46 32.43 41.08 37.62 3.07 a⁄ value 3.79 6.42 5.20 0.78 4.77 6.34 5.55 0.39 b⁄ value 21.01 27.07 23.27 1.94 11.02 14.01 12.47 0.88 WHC40a 4.14 5.20 4.91 0.36 5.39 6.55 6.10 0.33 WHC60a 4.81 5.85 5.23 0.33 5.59 6.72 6.34 0.33 WHC80a 5.15 6.50 5.88 0.34 6.65 9.26 8.19 0.68 OHC40b 0.69 0.85 0.76 0.04 0.78 1.06 0.93 0.08 OHC60b 0.68 0.80 0.76 0.03 0.92 1.05 0.98 0.04 OHC80b 0.95 1.17 1.03 0.06 1.07 1.39 1.28 0.08 Viscosity (mPa s) 46.73 60.07 54.24 4.38 66.80 83.90 76.47 5.56 BEF (N) 32.70 40.91 37.29 2.53 35.94 63.24 50.68 8.73 (b) Cavendish pulp flour Green (G-pulp) Ripe (R-pulp) pH 4.37 5.65 5.06 0.52 4.76 5.60 5.13 0.29 TSS (°Brix) 1.03 1.43 1.22 0.12 3.77 4.57 4.26 0.24 L⁄ value 64.37 79.25 74.18 4.62 67.12 74.86 70.85 2.53 a⁄ value 1.57 3.67 2.53 0.78 2.42 5.07 3.22 0.80 b⁄ value 14.69 21.69 17.36 2.32 11.51 20.23 14.15 2.59 WHC40a 3.72 4.08 3.94 0.12 1.08 1.69 1.37 0.18 WHC60a 5.37 5.99 5.66 0.17 1.56 1.88 1.71 0.10 WHC80a 6.03 6.53 6.31 0.17 3.99 5.03 4.67 0.41 OHC40b 0.64 0.91 0.80 0.09 0.69 0.87 0.79 0.05 OHC60b 0.42 0.64 0.50 0.07 0.73 0.87 0.82 0.04 OHC80b 0.71 0.97 0.85 0.06 0.94 1.15 1.05 0.07 Viscosity (mPa s) 35.07 47.47 40.94 3.65 84.13 91.67 87.88 2.18 BEF (N)e 0.54 0.81 0.67 0.07 1.97 2.72 2.32 0.20

a Water holding capacity (g water/g dry sample). b Oil holding capacity (g oil/g dry sample). c n = 12. d Standard deviation. e Back extrusion force.

Table 2 fibre-rich that could hold 2.2 g oil/g dry sample Multivariate test (MANOVA) for four different groups (G-peel, R-peel, G-pulp, and R- (Rodriguez-Ambriz et al., 2008), but are similar to that of mango pulp). dietary fibre with OHC in the range 1.0–1.5 g oil/g ((Larrauri Effect Test Value F Sig. et al., 1996). Other products tested for OHC by other researchers in- Group Pillai’s trace 2.94 123.48 <0.0001 clude mango peel dietary fibre (4 g oil/g), (Larrauri et al., 1996) Wilks’ Lambda 0.00 225.58 <0.0001 and citrus peel fibre (2.35–5.09 g oil/g) (Chau & Huang, 2003). Hotelling’s Trace 393.79 309.65 <0.0001 OHC relates to the hydrophilic character of present in Roy’s largest root 215.94 564.75 <0.0001 the flour (Rodriguez-Ambriz et al., 2008) that is present in high quantity in green flour (Rodriguez-Ambriz et al., 2008; Zhang et al., 2005), and in lesser quantity in ripe flour. Mean viscosity ranged between 41.0 and 87.9 mPa s, and the Table 3 Wilks’ Lambda for testing DFs. mean BEF ranged between 0.67 and 50.7 N. The order of viscosity and BEF was similar; R-pulp > R-peel > G-peel > G-pulp. The func- Test of function(s) Wilks’ Lambda P-value tionality of starch is largely related to its gelatinisation and pasting 1 through 3 0.000 <0.0001 characteristics. When flour sample was heated in water, starch 2 through 3 0.000 <0.0001 granules swell at their gelatinisation temperature, and when amy- 3 0.051 <0.0001 lose leaches out of the granules and swell, viscosity and textural

Table 4 The results of classification for discriminant analysis of the four groups.a

Group % Correct Predicted Group Membership Cavendish Green Peel Cavendish Green pulp Cavendish Ripe Peel Cavendish Ripe pulp Cavendish Green Peel 100 12 0 0 0 Cavendish Green pulp 100 0 12 0 0 Cavendish Ripe Peel 100 0 0 12 0 Cavendish Ripe pulp 100 0 0 0 12

a 100.0% of original grouped cases correctly classified. 316 A.F.M. Alkarkhi et al. / Food Chemistry 129 (2011) 312–318 changes result. In green flour, starch gelatinisation may contribute low in ripe banana peel (Emaga et al., 2007), the viscosity and to a certain extend to viscosity and texture. Since starch content is texture of ripe flour could have been attributed mostly by

(a) 25.00

20.00

15.00

10.00

5.00 Green Peel Ripe Peel Green Pulp 0.00 Ripe Pulp -20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 25.00 30.00

-5.00

-10.00 Scores of the second discriminant

-15.00

-20.00 Scores of the first discriminant function

(b) 6.00

4.00

2.00

Green Peel 0.00 Ripe Peel -20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 25.00 30.00 Green Pulp Ripe Pulp -2.00

-4.00 Scores of the third discriminant function

-6.00

-8.00

-10.00 Scores of the first discriminant function

(c) 6.00

4.00

2.00

Green Peel 0.00 Ripe Peel -20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 25.00 Green Pulp Ripe Pulp -2.00

-4.00

-6.00 Scores of the scores third discriminant

-8.00

-10.00 Scores of the second discriminant

Fig. 1. The scores of discriminant functions for (a) first and second (b) first and third, and (c) second and third, discriminant functions. A.F.M. Alkarkhi et al. / Food Chemistry 129 (2011) 312–318 317

hemicelluloses and pectin polysaccharides. This explanation is Z1 ¼0:15pH þ 0:82TSS 0:64L 0:06a þ 0:30b acceptable since banana peel contain a vast quantity of dietary fi- þ 0:54WHC40 þ 0:70WHC60 0:04WHC80 bre, mainly hemicelluloses and pectin polysaccharides (Emaga et al., 2007; Zhang et al., 2005). The total dietary fibre content of þ 0:47OHC40 þ 0:14OHC60 þ 0:40OHC80 banana peel can be as high as 50% (based on dry basis) (Emaga þ 0:16Viscosity þ 0:64Texture ð2Þ et al., 2007), while the hemicelluloses of banana peel constitute 20% of peel, and have solution properties (Zhang et al., 2005). Hemicelluloses of banana peel may even be further developed into Z2 ¼0:06pH þ 0:61TSS 0:15L þ 0:15a 0:04b gums or hydrocolloids (Zhang et al., 2005). The exceptionally high 0:31WHC40 0:43WHC60 0:22WHC80 viscosity of ripe flour was also attributed to its high sugar content as indicated by TSS, and protein contents since protein has been þ 0:12OHC40 þ 0:31OHC60 þ 0:24OHC80 shown to increase with increasing ripeness of banana cultivars þ 0:64Viscosity 0:12Texture ð3Þ (Yomeni et al., 2004). The differences in these functionalities may have implications in products incorporated with banana flours. Choice of flour to be used in product development will be based Z3 ¼ 0:47pH þ 0:27TSS þ 0:96L þ 0:87a 0:86b on these properties. For instance, flour prepared from ripe banana peel or pulp will be suitable for products requiring sugars, viscosity 0:25WHC40 þ 0:67WHC60 þ 0:18WHC80 and texture. These results also indicated the potentials of Caven- þ 0:14OHC40 þ 0:12OHC60 0:31OHC80 dish banana peel flour, together with banana pulp flour to be 0:10Viscosity 0:03Texture ð4Þ exploited as food ingredients. TSS, L⁄ values, WHC40, WHC60 and texture (BEF) exhibited strong contribution in discriminating the four flour groups and ac- 3.2. Multivariate analysis count for most of the expected variations in physicochemical prop- erties (Eq. (2)). Eq. (2) explains 54.8% of the variation between The results of MANOVA for physicochemical parameters are groups, while Eq. (3) explains only 40.5% of the variation, and this shown in Table 2. According to these results, the physicochemical amount belongs mainly to the contribution of TSS and viscosity, properties in all groups (G-peel, R-peel, G-pulp and R-pulp) exhib- whilst other parameters showed less contribution in explaining ited a strong significant difference in terms of selected parameters the variation between the groups. L⁄, a⁄, b⁄ values and WHC60 (P < 0.0001). These results indicate that flours prepared from peel exhibited strong contribution in discriminating the groups and ac- and pulp, using green and ripe banana are different based on count for 4.7% of the variation. It can also be seen that OHC40, physicochemical properties. Variation in physicochemical proper- OHC60, OHC80 and WHC80 did not show a strong contribution ties was evaluated through DA. Three DFs were found to discrimi- in all equations (Eqs. (2)–(4)). nate the four groups of flour (Eqs. (2)–(4)). Wilk’s Lambda test for The classification matrix for variety of banana (Table 4) showed validity of each discriminant function showed that DFs are statisti- that 100% of the cases were correctly classified to their respective cally significant (Table 3). Furthermore 100% of the total variance groups. The results of classification also showed that significant between the four groups was explained by three DFs. The relative differences existed between groups of banana flour, which are ex- contribution for each parameter in each DF is given below: pressed by in term of one DF (Eq. (2)).

Fig. 2. Dendrogram showing clustering of sampling sites based on physicochemical properties of banana peel and pulp flours produced using two different stage of ripeness. 318 A.F.M. Alkarkhi et al. / Food Chemistry 129 (2011) 312–318

Relationship between the scores of DFs and the samples studied References is depicted in Fig. 1a. Horizontal axis corresponded to the scores of the first DF, whilst the vertical axis corresponded to the second DF. Alvin, C. R. (2002). Methods of multivariate analysis. USA: John Wiley & Sons. INC.. Aparicio-Saguilan, A., Sayago-Ayerdi, S. G., Vargas-Torres, A., Juscelino, T., Ascencio- It could be seen from Fig. 1 that all the first DF was responsible for Otero, T. E., & Bello-Perez, L. A. (2007). Slowly digestible cookies prepared from discriminating pulp and peel flour, whilst the second DF was resistant starch-rich lintnerized banana starch. Journal of Food Composition and responsible in discriminating ripe and green flour. It can also be Analysis, 20, 175–181. seen that R-peel and G-peel flours are closer to each other com- Bugaud, C., Chillet, M., Beaute, M. P., & Dubois, C. (2006). Physicochemical analysis of mountain from the French West Indies. Scientia Horticulturae, 108, pared to R-pulp and G-pulp flour (Fig. 1b and c). This observation 167–172. has been explained in Table 1, i.e. the viscosity and TSS of G-peel Chau, C. F., & Huang, Y. L. (2003). Comparison of chemical composition and and R-peel flours were closer to each other compared to those of physicochemical properties of different fiber prepared from the peel of Citrus sinensis L. cv. Liucheng. Journal of Agricultural and Food Chemistry, 51, 2615–2618. G-pulp and R-pulp. Chen, C. R., & Ramaswamy, H. S. (2002). Color and texture change kinetics in In general, it can be concluded that TSS, L⁄ value, WHC40, ripening bananas. Lebensmittel-Wissenschaft und Technologie, 35, 415–419. WHC60 and BEF were useful in discriminating the peel and pulp Emaga, T. H., Andrianaivo, R. H., Wathelet, B., Tchango, J. T., & Paquot, M. (2007). Effects of the stage of maturation and varieties on the chemical composition of flour of Cavendish banana. TSS and viscosity were useful in dis- banana and plantain peels. Food Chemistry, 103, 590–600. criminating flour prepared from different stage of ripeness. How- Emaga, T. H., Robert, C., Ronkart, S. N., Wathelet, B., & Paquot, M. (2008). Dietary ever since major colour changes occurred during drying of the fiber components and pectin chemical features of peels during ripening in banana and plaintain varieties. Bioresource Technology, 99, 4346–43454. peel, the use of L⁄ value may be inappropriate for discriminating Fagbemi, T. N. (1999). Effect of blanching and ripening on functional properties of between pulp and peel flours. plantain (Musa aab) flour. Plant Foods for Human Nutrition, 54, 261–269. Gamlath, S. (2008). Impact of ripening stages of banana flour on the quality of extruded products. International Journal of Food Science and Technology, 43(9), 3.2.1. Cluster analysis 1541–1548. Cluster analysis (CA) was used to identify the similarity groups Juarez-Garcia, E., Agama-Acevedo, E., Sayago-Ayerdi, S. G., Rodriguez-Ambriz, S. L., & between the samples. CA rendered a dendrogram as shown in Bello-Perez, L. A. (2006). Composition, digestibility and application in Fig. 2, grouping all 48 samples into four statistically significant breadmaking of banana flour. Plant Foods for Human Nutrition, 61, 131–137. Larrauri, J. A., Ruperez, P., Borroto, B., & Saura-Calixto, F. (1996). Mango peels as a clusters. Cluster 1 (samples 1–12 for green peel (G-peel)), cluster new tropical fiber: Preparation and characterization. Lebensmittel-Wissenschaft 2 (samples 13–24 for ripe peel (R-peel)), cluster 3 (samples 25– und Technologie, 29, 729–733. 36 green pulp (G-pulp)), and cluster 4 (37–48 ripe pulp (R-pulp)). Markus, P. F., Elena, R. R., Jacinto, D. M., & Carlos, D. R. (2002). Statistical differentiation of bananas according to their mineral composition. Journal of This result reveals that the four groups have different characteris- Agricultural and Food Chemistry, 50, 6130–6135. tics in terms of physicochemical properties. This supports the re- Ranzani, T. D. C. M. R., Sturion, L. G., & Bicudo, H. M. (1996). Chemical and biological sults of MANOVA and DA, since the same result was obtained by evaluation of ripe banana peel. Archivos Latinoamericanos de Nutricion, 46(4), 320–324. these two techniques. This grouping gives evidence that samples Ricardo, C. R., Pablo, S. H., Elena, M. R. R., Jacinto, D. M., & Carlos, D. R. (2003). in each group share each other the sources of physicochemical Mineral concentration in cultivars of potatoes. Food Chemistry, 83, 247–253. properties. It implies that for rapid assessment and quality control Richard, A. J., & Dean, W. W. (2002). Applied multivariate statistical analysis. London: Prentice-Hall. of banana pulp and peel flour using physicochemical properties, Rodriguez-Ambriz, S. L., Islas-Hernández, J. J., Agama-Acevedo, E., Tovar, J., & Bello- only one sample in each group will be sufficient to represent the Pérez, L. A. (2008). Characterization of a fiber-rich powder prepared by flour prepared from parts of banana (pulp or peel) or banana from liquefaction of unripe banana flour. Food Chemistry, 107, 1515–1521. Rungsinee, S., & Natcharee, P. (2007). Oxygen permeability and mechanical different stage of ripeness (green or ripe). properties of banana films. Food Research International, 40, 365–370. Salvador, A., Sanz, T., & Fiszman, S. M. (2007). Changes in colour and texture and 4. Conclusion their relationship with eating quality during storage of two different dessert bananas. Postharvest Biology and Technology, 43, 319–325. Someya, S., Yoshiki, Y., & Okubo, K. (2002). Antioxidant compounds from banana Based on the physicochemical properties data and analysis, (Musa Cavendish). Food Chemistry, 79, 351–354. ´ multivariate statistical techniques can help in discriminating bana- Suárez, M. H., Rodrlguez, E. M. R., & Romero, C. D. (2007). Mineral and trace element concentrations in cultivars of tomatoes. Food Chemistry, 104, 489–499. na flour prepared from pulp and peel, and green and ripe fruits of Suntharalingam, S., & Ravindran, G. (1993). Physical and biochemical properties of Cavendish banana. TSS, WHC40, WHC60 and BEF were useful in green banana flour. Plant Foods for Human Nutrition, 43, 19–27. discriminating the peel and pulp flour, whilst TSS and viscosity Tchobanoglous, G., Theisen, H., & Vigil, S. (1993). Integrated solid waste management: Engineering principles and management issues. New York: McGraw-Hill. were useful in discriminating flour prepared from different stage Terra, N. N., Garcia, E., & Lajolo, F. M. (1983). Starch-sugar transformation during of ripeness. Future work should aims at studying similar tech- banana ripening: The behavior of UDP glucose pyrophosphorylase, sucrose niques of differentiation of banana peel flour produced from all synthetase and invertase. Journal of Food Science, 48, 1097–1100. stages of ripeness. Improved drying methods to yield better quality Thipayarat, A. (2007). Quality and physiochemical properties of banana paste under vacuum dehydration. International Journal of Food Engineering, 3(4), 1 (article 6). flour should also be researched. Waliszewski, K. N., Aparicio, M. A., Bello, L. A., & Monroy, J. A. (2003). Changes of banana starch by chemical and physical modification. Carbohydrate Polymers, Acknowledgements 52, 237–242. Yomeni, M. O., Njoukam, J., & Tchango Tchango, J. (2004). Influence of the stage of ripeness of plaintains and some cooking bananas on the sensory and The authors gratefully acknowledge the financial assistance physicochemical characteristics of processed products. Journal of the Science of from Universiti Sains Malaysia and the research facilities by Dean Food and Agriculture, 84(9), 1069–1077. Zhang, P., Whistler, R. L., BeMiller, J. N., & Hamaker, B. R. (2005). Banana starch: of the School of Industrial Technology, USM, Penang. USM short production, physicochemical properties and digestibility – a review. term grant (304/PTEKIND/638098) is acknowledged. Carbohydrate Polymers, 59, 443–458.