The soluble fiber content, which can be fermented in the colon, is significantly lower in carob and this portion contains simple carbohydrates
[14][82].
-
The total sugar content in carob pulp typically ranges from 30 to 60%. Sucrose forms the largest portion of these sugars, contributing 65–75% of the total sugar content. The remainder of the sugar content is mostly made up of the monosaccharides fructose and glucose, contributing 15% and 25% of the total sugars, respectively
[25][93]. Carob pods are especially notable for their high sugar content, which is even higher than that of beets or sugar cane (about 200 g/kg)
[26][94]. Carob seeds, on the other hand, primarily contain the sugars sucrose (8.1 ± 0.04%) and glucose (2.2 ± 0.01%). They also contain various monosaccharides following polysaccharide hydrolysis, namely mannose (54.0 ± 0.50%), galactose (15.5 ± 0.14%), glucose (2.2 ± 0.01%), arabinose (1.0 ± 0.00%), and xylose (0.4 ± 0.00%). Fructose was not detected
[27][95].
Carob is a good source of protein, and its protein content is particularly rich in both essential and non-essential amino acids. The protein fraction in carob seeds, for instance, has a substantial amount of the non-essential amino acids like arginine (27.8 ± 0.25 g/100 g) and alanine (17.0 ± 0.16 g/100 g) and the essential amino acid lysine (15.0 ± 0.14 g/100 g). Moderate amounts of essential amino acids like isoleucine (8.6 ± 0.08 g/100 g) and valine (7.3 ± 0.06 g/100 g) are also present in carob seeds
[27][95]. In terms of the overall amino acid content in carobs, it is composed of a mixture of 17 residues including aspartic acid, glutamic acid, serine, glycine, histidine, arginine, threonine, alanine, tyrosine, valine, proline, methionine, isoleucine, leucine, cysteine, phenylalanine, and lysine
[28][29][96,97]. In particular, aspartic acid, asparagine, alanine, glutamic acid, leucine, and valine make up approximately 57% of the total amino acid content of the pods
[30][98]. Ground carob flour contains about 4.45% protein, with carob germ flour proteins including albumin and globulin (32%) and glutelin (68%)
[28][96]. Importantly, no prolamins are detected in carob germ flour proteins
[31][99], which contributes to the gluten-free property of carob
[32][100]. Carob seeds are characterized by high protein content (25.7 ± 0.18%). Even in naturally grown carob seeds, like those from the Tazmalt region in northern Algeria, a moderate protein content was reported (18.6 ± 0.3%)
[33][101]. Carob leaves also have a balanced nutrient composition. A proximate analysis based on dry weight showed the presence of carbohydrates (16.62%), fat (4.60%), protein (22.25%), ash (4.255%), and dietary fibers (11.77%)
[34][102].
According to research by Özcan et al., 2007
[35][103], the protein, oil, crude fiber, ash, and energy values of carob fruit and carob flour were found to be not statistically different. However, carob syrup showed lower values for protein, crude fiber, ash, and energy compared to both carob fruit and carob flour. Interestingly, carob syrup had the highest total sugar content, with 48.3% in the fruit and 41% in the flour. Carob pods from the eastern parts of Sicily in Italy, as reported by Avallone et al., 2002
[17][85], had the following composition (dry weight): moisture (6–10%), ash (1–6%), protein (1–5%), fat (0.4–0.8%), sucrose (27–40%), D-glucose (3–5%), D-fructose (3–8%), and starch (0.1–1.3%). The carob germ which consists of fine fragments of hull and endosperm, and could be obtained industrially, has the following composition: 8.3% moisture, 6.5% ash, 6.6% lipids (neutral and polar) which contain approximately 21% polar lipids, 54.7% crude proteins, and an energy value of 17.5 kJ/g
[36][104]. Moreover, the average proximate composition of raw carob pods is as follows: 8.17–9.56% moisture, 89.57–91.12% carbohydrates, 40.69–54.74% total sugars (33.70–45.09% sucrose, 1.79–4.95% glucose, and 1.80–5.19% fructose), 29.88–36.07% dietary fiber, 3.07–4.42% protein, 2.58–3.08% polyphenols, 0.45–0.86% fat, and 2.13–2.69% ash
[37][17].
The mineral content of carob varies depending on the part of the tree analyzed (leaves, bark, integument, pulp) and the specific variety of the carob tree (
C. siliqua L.), such as spontaneous female, spontaneous male, and grafted female. In a study conducted in Chefchaouen, northern Morocco, it was found that calcium (Ca) generally appears to be the most prevalent mineral in the leaves and bark of the carob tree, regardless of the category studied. Other detected elements in significant amounts include potassium (K), magnesium (Mg), sodium (Na), phosphorus (P), chlorine (Cl), copper (Cu), iron (Fe), zinc (Zn), and selenium (Se). It was also demonstrated that while potassium (K) was the main macronutrient in the bark, leaves had higher concentrations of other minerals such as calcium (Ca), magnesium (Mg), phosphorus (P), and zinc (Zn). Conversely, for copper (Cu), iron (Fe), and selenium (Se), the bark had higher levels
[38][105]. A separate study of Anatolian carob pods by Ayaz et al. (2009) discovered the following mineral concentrations: 970 mg/100 g K, 71 mg/100 g P, 300 mg/100 g Ca, 60 mg/100 g Mg, 1.88 mg/100 g Fe, 1.29 mg/100 g manganese (Mn), and 0.85 mg/100 g Cu
[30][98]. Furthermore, research on both wild and grafted carob trees in the province of Antalya in Turkey showed that the pods and seeds of the grafted carob trees generally had higher mineral concentrations than their wild counterparts. In all the samples, potassium was the most prevalent mineral, with the highest concentration found in the pods of the wild carob fruit. Of the micro-minerals, iron was the most abundant in the seeds of grafted carob fruits
[39][106].
The study by El Bouzdoudi et al., 2017
[40][107] on carobs grown in Morocco identified five macroelements (potassium, calcium, chlorine, magnesium, and sodium) and thirty microelements (iron, aluminium, strontium, rubidium, copper, zinc, manganese, zirconium, barium, thorium, bromine, thulium, chromium, selenium, cerium, lanthanum, caesium, antimony, neodymium, mercury, cobalt, arsenic, scandium, molybdenum, tantalum, gold, hafnium, samarium, silver, and europium) in the whole pod, pulp, and seed and other constituents. The detection of these mineral elements in such a wide variety underscores the role of carob as a valuable source of essential nutrients, contributing to its longstanding use in human and animal diets. Moreover, the study by Khlifa et al., 2013
[25][93] examining carob pods from the Chefchaouen region in northern Morocco indicated a low-fat content in the carob pod. Another study on carob seeds from Malaga, Spain, which involved treating the seeds with acid or hot water to isolate the carob germ meal, revealed the presence of polar lipids accounting for 13–24% of the total lipid content (1.1–1.7% of carob germ meal). This lipid fraction primarily consisted of oleic acid (34.4%) and linoleic acid (44.5%) as the major fatty acids, with palmitic acid (16.2%) and stearic acid (3.4%) being the main saturated fatty acids
[36][104]. According to Fidan et al., 2020
[27][95], the lipid fraction content of carob seeds was determined to be around 2.1%, consisting of non-saponifiable lipids (17.2 ± 0.13%), sterols (4.0 ± 0.04%), phospholipids (7.2 ± 0.07%), and tocopherols (2801.0 ± 40.16 mg/kg). They identified 11 fatty acids that constituted the total oil content, with oleic (45.0 ± 0.42%) and linoleic (32.4 ± 0.30%) acids being the most abundant. Palmitic (16.6 ± 0.15%) and stearic (4.7 ± 0.15%) acids were also present in moderate amounts. Research by Dallali et al., 2018
[41][108] on Tunisian carob tree leaves found a fatty acid profile dominated by unsaturated fatty acids. Among the 12 common fatty acids identified, linolenic and linoleic acids were the most prevalent.
Table 13 groups the chemical compounds present in the different parts of the carob tree including the leaves, pods, pulp, and seeds.
Table 13.
Chemical composition of carob (
C. siliqua
L.).
Class |
Compounds |
Part of the Plant |
References |
Phenols |
Resorcinol |
Leaves, pods, pulp, seeds |
[34][102] |
Vanillin, fraxidin, 2,4- bis(dimethylbenzyl)-6-butylphenol |
Leaves |
[34][42][102,109] |
Alizarin, hydroquinone, lignan bis(trihydroxyphenyl)methanone |
Pods |
[43][44][110,111] |
Phenolic acids |
Gallic acid, chlorogenic acid, syringic acid, ferulic acid, coumaric acid, cinnamic acid |
Leaves, pods, pulp, seeds |
[4][5][21][34][43][44][45][46][47][48][49][[57][58][59][60]][4,5[,8950][51][52][53][54][55][56]61],102[62],110[,11163,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130] |
4-Hydroxybenzoic acid, caffeic acid, vanillic acid, gentisic acid |
Leaves, pods, pulp |
[5][21][34][45][46][47][52][54][55][58][59[62][5,89][,10260][,11261,113,114,119,121,122,125],126,127,128,129] |
Tannic acid |
Leaves, pods, seeds |
[4][55][4,122] |
Ellagic acid, rosmarinic acid |
Pods, pulp, seeds |
[44][52][58][59][60][111,119,125,126,127] |
Sinapic acid |
Pulp, seeds |
[44][59][111,126] |
Pyrogallol, methyl gallate, benzoic acid, protocatechuic acid |
Pods, pulp |
[4][5]5[43][44][52][53][55],110[,11161,119][,12062][4,,122,128,129] |
Quinic acid |
Leaves, pods |
[42][53][109,120] |
Transferulic acid, O-feruloylrutinose, O- feruloylrutinose isomer, p-coumaroyl- galloylhexose, O-p-coumaroylrutinose, siliquapyranone |
Pods |
[43][53][58][110,120,125] |
4-Hydroxy-coumaric acid |
Leaves |
[45][46][112,113] |
5-Caffeoylquinic acid, myristic acid, ascorbic acid |
Pulp |
[44][59][64][111,126,131] |
Flavonoids |
Epicatechin, quercetin, kaempferol, luteolin, catechin, apigenin |
Leaves, pods, pulp, seeds |
[4]4[5][21][34][43][44][45][46][48][49][51]][59][60][61][,563,89],102[52][53][64,110[54][55][][65][,111,112,113,115,116,118,119,120,12156],122[57],123[,12458,125,126,127,128,130,131,132] |
Epigallocatechin gallate, rutin, myricetin, naringenin |
Leaves, pods, pulp |
[4][5][43][44][45][46],11157,112[47][49][50][51][52],113],114[53][54][56][[58,116][59,117][60][61][4,5,110,118,119,120,121,123,124,125,126,127,128] |
Iso-rhamnetin |
Leaves, pods, seeds |
[34][43][44][52][58][102,110,111,119,125] |
Leucoanthocyanins |
Leaves, pulp, seeds |
[66][133] |
Genistein |
Leaves, pods |
[5][52][5,119] |
Quercitrin, catechin tannins |
Leaves, pulp |
[45]112[46][,11348][,11560][66][,127,133] |
Anthocyanins |
Pods, pulp, seeds |
[5][67][68][5,134,135] |
Myricitrin, daidzein, flavonol, morin |
Leaves |
[34][45][46][47][49][102,112,113,114,116] |
Rhamnosides, chrysoeriol, tricetin dimethyl ether, (iso)schaftoside-4′-O- glucoside, gallocatechin, chrysoeriol-O- deoxyheoxoside, dihydroxyflavanone hexoside, tetrahydroxy flavanone, trihy- droxy flavone (apigenin isomer), kamp- feride, methoxykampferol, dihydroxy flavanone, tricetin dimethyl ether, cirsi- liol, flavone glycosides, hydroxytyrosol |
Pods |
[5][43][52][53][55][5,110,119,120,122] |
Crismaritin, catechol, isoquercetrin, flavonols 3′,4′,5,7-OH, 2-hexadecanol scutellarin tetramethyl ether, silybin B, hydroxytyrosol, catechin gallate |
Pulp |
[4][59][62][64][4,126,129,131] |
Apigenin flavone, chrysin aglycones |
Seeds |
[52][119] |