The main objective of this research was to compare physicochemical parameters, antioxidant activity, lipid composition, and sensory analysis of initial and roasted carob pod powder (
Carob was spread in recent times to other Mediterranean-like regions such as California, Arizona, Mexico, Chile, and Argentina by Spaniards, to parts of Australia by Mediterranean emigrants and to South Africa and India [
Ripe carob pod is brown and contains 10–20% of carob kernels or seeds and 80–90% of carob kibbles [
In recent years, carob pulp which is a byproduct is becoming more popular for its organoleptic properties, aroma, color, and taste, and also for its dietary quality. Having a cocoa-like aroma of roasted carob, carob pulp is mainly roasted and grinded to powder to be used as cocoa substitute. Unlike cocoa powder, carob is free from the two stimulants caffeine and theobromine [
The objective of this work is valorization of carob pulp, which is a byproduct of processing carob to get seeds for carob gum, into roasted carob powders which could be used directly or as a raw material for producing aromas. This global study aims to compare physicochemical parameters, antioxidant activity, lipid composition, sensory analysis of initial and roasted carob powders obtained at different roasted temperatures. This study will permit investigating the possible synergistic effects of the mentioned parameters on final roasted carob powder.
Ripe carob pods were harvested from Tlemcen region, west Algeria. The fruits were cleaned, mixed, and crushed and the seeds were removed. Then, the carob kibbles were roasted at different time/temperature conditions in an artisanal roaster (Figure
Roasting process of carob pulp.
To determine the moisture, an aluminum cup was filled with about 1 g of extract and placed in an infrared balance (Sartorius MA 150, France), which is based on the thermogravimetric principle. In the beginning, the initial weight of the sample was recorded and afterwards, the sample was dried using an infrared lamp. An integrated balance measured the weight of the aluminum cup, continuously. The overall weight loss was interpreted as the corresponding humidity.
The aw value was measured using the VSA (Vapor Sorption Analyser, AQUALAB, France). 300 mg of powder was placed in an inox cup, which was then introduced into the device, and the aw was determined by using a chilled
After calibration of the pH meter Hanna HI2002, the pH samples of different powders were measured in triplicate. The concentration of each solution was at 10% m/v.
The color of the products was measured using the Chromameter Konica Minolta CR
The phenol-sulphuric acid method known by Dubois method was used to evaluate total sugars of unroasted carob and different roasted powders. Five grams of each powder was mixed with 50 mL of water with Ultra-Turrax and then passed to centrifugation. The supernatant was transferred into tubes by PIPETMAN to avoid any floating particles and diluted at 1/500 to obtain the adequate values comparing to the standards of glucose values. 2 mL of diluted solution was put in tube containing 1 mL of phenol 5% and then, 5 mL of concentrate sulphuric acid was added and left in water bath at 25–30°C for 20 min. These tubes were immediately cooled at 20°C with tap water. The absorbance was measured at 485 nm with spectrophotometer Jenway 700 against the blanks. Phenol correction was done against a solution containing 2 mL of water added by 1 ml of phenol 5% and 5 mL of sulphuric acid. The glucose assay was also prepared with the known concentrations from 0,025 g/L to 0,1 g/L. A standard curve of corresponding absorbance was drawn.
An enzymatic method was used to determine biochemically different sugars, like sucrose, glucose, and fructose with enzymatic kits (Biosentec, France).
The concentration of D-glucose/D-fructose/sucrose in the sample, used in the assay procedure, had to be between 0.05 and 0.8 g/L, wavelength 340 nm, optical path 1 cm, and temperature 20–37°C.
Three grams of each sample was weighted in crucibles which has to be preashed and was put in muffle furnace at 550°C for 5 hours. After incineration, the crucibles were left in desiccator for 30 mn and then weighed. The content of total ash is calculated as percentage relative to dry matter.
Five grams of each powder was mixed with 2 times 50 mL of methanol/water (80/20) with Ultra-Turrax for 7 min and then passed to centrifugation. The supernatant was transferred into the flasks and completed at 100 mL. The total phenolic content was evaluated by using the Folin-Ciocalteu method. Twenty microliters of the extract was mixed with 100
The radical scavenging activity of extract was evaluated by a modified version of the method, proposed by Brand and Williams, converted into micro method. More specifically, a stock methanolic solution (10 mg/mL) of each extract was diluted to prepare the samples, ranging from 20 to 0.625
Results are expressed as inhibitory concentration (IC50) which corresponds to extract concentration (
For CSE, 100 g of carob was placed in the extraction chamber of a Soxhlet apparatus (125 mL capacity). The cellulose thimble was plugged with cotton in order to avoid transfer of sample particles in the distillation flask. The Soxhlet apparatus, fitted with a condenser, was placed on a 2000 mL boiling flask, containing 1000 mL of solvent. Extraction was performed using a solid to liquid ratio of 1 to 10 (m/v), for 8 hours. After extraction, the extract was concentrated until being dried by solvent evaporation under vacuum (Laborota 4001, Heidolph, Germany) and finally, it was conserved at 4°C before analysis. Detailed analysis has been explained and detailed in our previous publication (Meullemiestre et al. 2016) [
Lipid classes in oil extract were determined by high-performance thin-layer chromatography (HPTLC), using two different development chromatography methods to separate polar and neutral classes. Lipids were quantified by a CAMAG 3 TLC scanning densitometer (CAMAG, Muttenz, Switzerland) with identification of the classes against the known polar and neutral lipid standards. Lipid classes of each carob extract were identified and quantified against those of corresponding lipid standards. Detailed analysis has been explained and detailed in our previous publication Meullemiestre et al. 2016 [
FAMEs were prepared from the lipid extract, using acid-catalyzed transmethylation. 1 mL of methanolic sulphuric acid (5%) solution was added to a specific amount of extracted carob oil. Triheptadecanoin (C17:0 TAG) was used as internal standard. Detailed analysis has been explained and detailed in our previous publication (Meullemiestre et al.) 2016 [
Fatty acids methyl esters were separated, identified, and quantified by gas chromatography, coupled with flame ionization detector (GC-FID). The instrument Agilent (Kyoto, Japan) was equipped with a BD-EN14103 capillary column 30 m × 320
Sensory analyses were conducted by a panel consisting of 18 graduate students from the University of Avignon, France. The subjects were seated in sensory booths with appropriate ventilation and lighting. The samples were presented to each panelist on white polystyrene plates. Subjects were instructed to place the stimuli on the tongue and rub the tongue against the palate. Tap water was supplied to the panelists for rinsing between samples. The following attributes were evaluated for the three products: roasted aroma, cacao aroma, sweet taste, astringent taste, and caramelised taste. For overall quality, the scale range was from 0 to 10. On this scale, a score of 0 represented the weakest attribute and a score of 10 represented the strongest one. Detailed analysis has been explained and detailed in our previous publication (Pingret et al. 2011) [
By roasting the carob pulp under different conditions of roasting time-roasting temperature combinations, the obtained product can have different specifications such as modulated color, aroma, and taste. Studying the effects of these parameters and the physicochemical ones allows the food industries to control the process for obtaining the best products.
Roasting has been done at different temperatures for the same processing time (20 min) to obtain different products in terms of color, aroma, and taste. The initial grinded carob pulp, C0, was just dried at 110°C to obtain the first product, C1, which has a lighter color and the specific initial carob odour. At 130°C, carob sugars undergo the Maillard reaction and the caramelisation, producing a new product, C2, which is obviously different from the unroasted one. Roasting at high temperature (150°C), the last product, C3, was completely dark as a result of producing brown pigments. The overall experimental plan is shown in Figure
Multidisciplinary study of roasting carob pulp.
Different parameters as moisture, water activity, total sugars, and different sugars as sucrose, glucose, and fructose have decreased when the temperature of roasting increases. The results are shown in Table
Physicochemical characterization of initial and roasted carob pod powder.
C0 | C1 | C2 | C3 | |
---|---|---|---|---|
Moisture (%) | 9 ± 0.8 | 6.3 ± 0.6 | 4.3 ± 0.8 | 3.5 ± 0.7 |
Aw | 0.6 ± 0.05 | 0.2 ± 0.05 | 0.155 ± 0.05 | 0.14 ± 0.05 |
pH | 5.6 ± 0.1 | 5.5 ± 0.1 | 5.4 ± 0.1 | 5.5 ± 0.1 |
Total sugars (%) | 43.4 ± 0.5 | 36 ± 0.5 | 27.3 ± 0.4 | 15.4 ± 0.5 |
Sucrose (%) |
27.6 ± 0.2 |
23.3 ± 0.2 |
10.5 ± 0.2 |
6.2 ± 0.2 |
Coloration |
22.6 ± 0.5 | 23.1 ± 0.5 | 20.7 ± 0.5 | 16.9 ± 0.5 |
The average moisture content of nonroasted carob powder samples was determined as 9% which reduced to 6.3%, 4.3%, and 3.5% after 20 min of roasting at 110°C, 130°C, and 150°C, respectively. These values are intermediate between carob moisture values of Sahin et al. 2009 [
Maillard reaction requires temperatures superior to 50°C and it is favoured when pH is around 4–7 while caramelisation proceeds at temperatures superior to 120°C and pH between 3 and 9 [
Carob is sweet product due to its content of total sugars; mostly sucrose, glucose, and fructose decrease more and more with the temperature and the time of roasting. Roasted carob C3 is less sweet than the natural carob. The ratio of individual sugars to total sugar in carob was similar in the three-roasted carob. The sweetness values decreased as the roasting temperature increased. Heating sucrose in concentrated solution at high temperature leads to hydrolysis and production of fructose and glucose. These components participate in different reactions of caramelisation to form stable 5-hydroxymethylfurfural (HMF) [
Phenolic compounds are of high interest as alternative for synthetic antioxidant to prevent lipid peroxidation in food products. Total polyphenol content (TPC) extracted from carob powder by Ultra-Turrax (
Total polyphenol content (TPC).
The obtained TPC increased by increasing the roasting temperature of 110°C, 130°C, and 150°C, respectively. C0 contains 0.51% a percentage in concordance with Sahin et al. 2009 [
The antioxidant potential of the extracts is shown in Figure
IC50 values determined by the DPPH assay for carob extracts obtained by Ultra-Turrax.
Comparing TPC to AA (antioxidant activity) data obtained from the extracts, it can be observed that AA was proportional to TPC. A high antioxidant activity is expected to be caused by its high content in polyphenols. Sahin et al., 2009 [
Folin-Ciocalteu reagent detects all phenolic groups present in sample, containing the naturally occurring phenolic and also the newly formed compound during roasting process. MRPs with phenolic type structure can also be determined by the Folin method. The increase in the TPC of the carob powders could be explained by the formation of MRPs with phenolic type structures during the process. The increase in the antioxidant activity of carob with increasing roasting degree was attributed to Maillard reaction products (MRPs) formed during roasting of carob like roasting coffee [
Since no standardized method is available to evaluate the antioxidant capacity of plant extracts and numerous methods have been employed to estimate the antioxidant potential, in the present study, DPPH radical scavenging effect was used to assess the antioxidant activity of carob powder before and after roasting.
The antioxidant activity (AA) of the extracts is due to the presence of phenolic compounds [
The different roasted carobs were also compared by their physical characteristics as color (Table
Color assessment of initial and roasted carob pod powders.
Roasted and unroasted carob were extracted with hexane for 8 hours by Soxhlet extraction. The extracts were centrifuged and evaporated. The obtained oil was analyzed by high-performance thin-layer chromatography (HPTLC) to gain the lipid classes. For obtaining fatty acid profiles, the gas chromatography coupled with a flame ionization detector (GC/FID) was used after transmethylation.
Carob oils were classified into two categories according to their polarities: neutral lipids and polar lipids. Carob oils tend to accumulate neutral lipids, including monoacylglycerol (MAG), diacylglycerol (DAG), triacylglycerol (TAG), free fatty acids (FFA), and alkyl chain. Using the high-performance thin-layer chromatography (HPTLC), neutral lipids of the extracted carob oils were separated and quantified. For all extracted carob oils, the distribution of the different lipid classes was obtained by the external calibration. To quantify the percentage of the lipid classes, four standards were used, including monoglycerides (MAG), diacylglycerol (DAG), triglycerides (TAG), and free fatty acids (FFA) (C18), and deposited on the HPTLC plate. As shown in Figure
Lipid composition.
As shown in Figure
Roasted carob has potentialities to be a dietary replacement of cocoa due to its lower content in fat and its good content in dietary fiber [
The results of sensorial tests for the three carobs are correlated with their physical characteristics in Figure
Sensorial analysis.
Berna et al. [
The effect of temperature on physicochemical parameters, antioxidant activity, lipid composition, and sensory analysis of unroasted and roasted carob powders were compared in this study. The initial carob powder (C0) was dried at 110°C (C1), 130°C (C2), and 150°C (C3) for the same processing time (20 min). The pH of the roasted products decrease just a little but the color of the products became darker, the average moisture content of C0 was reduced from 9% to 6.3% and 4.3% and 3.5%, and the water activity and the sweetness values decreased as the roasting temperature was increased. Total polyphenol content and the antioxidant activity which is due to the presence of the phenolic compounds, Maillard reaction, and caramelisation products increased by increasing the roasting temperature. Carob oil analysis showed that lipid yields decreased at higher roasting temperatures. They tended to accumulate neutral lipids, including monoacylglycerol, diacylglycerol, triacylglycerol, free fatty acids, and alkyl chain. Diacylglycerol and free fatty acids were the major components of all the extracted carob oils, with a decrease in the percentage of diacylglycerol and an increase in the percentage of free fatty acids as the roasting temperature increased. Fatty acid profiles showed that oleic acid, linoleic acid, and palmitic acid were mainly present in carob oil and represented at least 90% of the total extract. The panelists found C1 to be sweeter, have more caramel-like taste, and have more cacao-like aroma than the other ones and the most astringent taste, coffee-like aroma, and roasted aroma in C3. Roasted carob powder could be used as food ingredient in different kinds of food and also as dietary supplement.
The authors declare that there are no conflicts of interest regarding the publication of this paper.