M. E. S. Pardo et al.
2. Materials and Methods
2.1. Raw Materials: Treatment and Classification
The residues were dehydrated in a horizontal drying chamber (Lumisell, Mexico, Mexico) at 60˚C moisture
content was less than 10%.
2.2. Proximate Chemical Analysis of Raw Materials
Proximate chemical analysis for pulp and residues (leaf bracts, shell and core), was performed using the Associ-
ation of Official Analytical Chemists (AOAC) [2]. The total protein was determined [% N × 6.25] using method
993.19; total ash using method 955.04; crude fat using (method 920.39), moisture content using method 934.01,
crude fibre using the acid-alkaline hydrolysis method 991.42, carbohydrates were determined (by subtration as
the nitrogen-free extract, NFE).
The Insoluble (IDF) and soluble (SDF) dietary fibre contents were determined according to the AOAC me-
thod. The samples were dried, defatted and freed from carbohydrate, before the analysis. The (TDF) contents
were corrected for residual protein, and ash. The total dietary fibre content was calculated as the sum of IDF and
SDF.
Total dietary fibre (method 991.43) was performed according to the technique described in AOAC [2]. The
samples were dried, defatted and free of carbohydrate. It was run blank through entire procedure along with
samples to measure any con tribution reagents to re sidue. In triplicate, 1 ± 0.1 g of sample were suspended en 50
mL of phosphate buffer pH 6.0; submitted to enzymatic hydrolysis by 50 µL of heat stable α-amylase (A-3306,
Sigma Chem. Co. St. Louis MO, USA) in boiling water bath for 30 min. After cooling suspension to room tem-
perature, pH was adjusted to 7.5 ± 0.1 and 100µL of protease (P-3910, Sigma Chem. Co. St. Louis MO, USA)
was added and left to in water bath at 60˚C for 30 min. After cooling pH was adjusted to 4.5 ± 0.1 and 300 µL of
amyloglucosidase (A-9913 Sigma, Chem. Co. St. Louis MO, USA) we re a dde d.
The suspension was left to in water bath at 60˚C for 30 min. After that it was filtered to obtain the supernatant
and the insoluble fr action. The supernatant was precip itated with 95% alcohol to precipitate the SD F and it was
quantified by drying overnight at 105˚C. The insoluble fraction was washed with 78% and 95% alcohol solu-
tions and acetone, respectively, followed by drying overnight at 105˚C to obtain the IDF. The dietary fibre con-
tents were corrected for residual protein, ash and blank. The total dietary fibre was indicated as the sum of IDF +
SDF.
To quantify the content of hemicellulose, the method for the determination of the neutral detergent fibre (NDF)
content was used as described previously by Van Soest [3]. Consequently, this residue of this analysis was util-
ized to determine the content of cellulose and lignin called the acid detergent fibre (ADF), using method 973.18.
2.3. Statistical Analysis of Data
An analysis of variance was used applying Tukey’s test (α = 0.05) utilizing Statistical Analysis System 8.0 (SAS
Institute Inc., Cary, Nort h California , US A) software [4].
3. Results and Discussion
In Table 1 the proximate chemical composition of the pineapple pulp and residues (leaf bracts, shell and core) are
shown. Statistical analysis revealed significant differences (p ≤ 0.05) i n the parameters t ota l protein, a s h a nd c rude
fat values. The total protein content ranged from 0.7 g/100g of leaf bracts to 1.58 g/100g of pulp; this total protein
could be mainly attributed to hydroxyproline-rich glycoprotein, Because Bartolome and Ruper ez [5] an d Smith et
al. [6] repo rted that the glycop roteins in the sh ells of fruits, are immersed in the primary cell wall forming a net-
work of microfibr ils w ith th e cellulo se [7]. The leaf bracts exhibited th e highest ash content, w hich was twice th at
in the pulp; although the values reported by Chau and Huang [8] in orange peels (3.3 g/100g) are twice those of
the pineapple’s shell and core. One important consideration is that carbohydrate content was determined by cal-
culation and may include simple sugars such as monosaccharides and disaccharides [9]. The highest content of
crude fat was found in the edible fraction of the pulp, followed by the core (in the case of the residue), whereas
the lowest concentration of crude fat was in the leaf bracts.