Banana meal
The concentration of most nutrients in the two sources of banana meal (
Table 1) was within the range of expected values, but crude protein and ash were greater, and starch was less than published values [
3,
4,
7–
9]. The variation in chemical composition among sources of banana meal is due to tropical and subtropical countries having different varieties of banana, as well as differences in climate, soil type, and harvesting time, which may result in different degrees of ripeness of the bananas [
10,
11]. Processing of the harvested bananas may also be distinct among different sources of banana meal. Therefore, it is possible that the bananas used to produce banana meal used in this study were at a riper stage than the bananas used in previous studies because starch decreases with maturation [
11]. Differences between the two banana meal samples also indicate that sample 1 was originated from unpeeled bananas, whereas sample 2 was from peeled bananas because banana peel contributes to greater fiber levels, which dilute the percentage of starch in the sample [
12]. The high ash level in both samples indicates soil contamination.
The total analyzed components of banana meal were close to 100%, indicating that most nutrients in these ingredients were accounted for [
13]. The high coefficient of variation for some of the analyzed nutrients indicates that the ripeness stage or banana variety influenced the chemical composition of the samples. As an example, total dietary fiber is nearly twice as high in one sample than in the other, particularly insoluble dietary fiber. However, the variation in fiber content is consistent with published values for various banana varieties [
4,
7]. Glucose and fructose were the sugars analyzed in the greatest concentrations, but maltose and sucrose were also present in one of the samples.
Banana meal, with or without peel, can be fed to all types of livestock. Aside from carbohydrates, banana meal contains a significant amount of minerals, particularly potassium, but is low in sulfur-AA, as demonstrated in this study, which is consistent with previous data [
9]. In addition, banana contains polyunsaturated fatty acids (primarily linoleic and linolenic acid) that can act as antioxidants, but it may also contain anti-nutritional factors such as tannins (in the peels), oxalate, mycotoxins, and pesticides [
9,
11].
Bananas that are in fresh or ensiled forms are more commonly used for ruminants, but banana meal can also be used as a source of starch or a lactose substitute in calf diets [
9,
14]. Banana meal can also be used to replace cereal grains in diets for growing pigs at a maximum inclusion of 25%, but due to the low protein content, diets containing banana meal must be supplemented with additional AA sources. In addition, high levels of banana meal for pigs may cause a negative impact on growth performance due to unbalanced nutrient composition, palatability issues, or the presence of tannins [
9]. In diets for poultry, banana meal should not exceed 10% of the grain content because it may be detrimental to growth performance [
15].
Rice bran
The chemical composition of full-fat rice bran from different countries (
Tables 2 and
3) was within the range of published values [
16–
19], but the concentration of AEE ranged from 9% to 20% indicating that some of the ingredients sold as full-fat rice bran had been partially defatted. Likewise, the chemical composition of defatted rice bran (
Table 4) was within the range of published data [
16–
19]. However, when compared with values from previous studies, defatted rice bran from Indonesia had a slightly greater AEE content and a lower crude protein content.
Samples of full-fat rice bran from Australia had greater (p<0.05) concentrations of AEE, lysine, and glycine compared with samples from the Philippines and Vietnam (
Table 5). Full-fat rice bran from Australia and Thailand had greater (p<0.05) concentrations of gross energy, isoleucine, leucine, phenylalanine, threonine, valine, alanine, aspartic acid, proline, and serine than sources of full-fat rice bran from Vietnam. When compared with all other countries, full-fat rice bran from Australia had greater (p<0.05) concentrations of tryptophan and manganese, whereas full-fat rice bran from the Philippines contained less zinc (p<0.05) than all other sources.
The observation that there was variation in chemical composition among samples of full-fat rice bran or defatted rice bran produced in different countries may be a result of differences in growing conditions, rice variety, the nature and quality of the bran due to milling condition processes, or hull contamination [
20,
21]. Gross energy in full-fat rice bran samples ranged from 3,918 to 4,814 kcal/kg, which likely is a result of the indication that some samples were partially defatted. As a result, many products labeled “rice brans” are mixtures of co-products obtained at various stages of the milling process, resulting in variation in chemical composition. As a consequence, frequent analysis of nutrients in rice bran is needed, especially when using higher levels of rice bran in the diets [
1]. Differences in mineral concentration may also be a result of differences in soil mineral concentrations or rate of fertilization.
Economic factors such as agricultural credit, support policies, input availability (fertilizers, seeds, or pesticides), research, and knowledge transfer have an impact on production of rice and may also contribute to differences in the composition of rice bran among countries [
22]. As an example, the reason full-fat rice bran from Vietnam may contain more insoluble dietary fiber than samples from other countries may be due to the type of production involved because rice mills in Vietnam sometimes mix rice husk fragments with rice bran, resulting in a greater content of total dietary fiber in these samples [
23]. Nevertheless, the analyzed components in the rice co-products included in this study were close to 100%, indicating that all nutrients in these ingredients were accounted for [
13].
Full-fat rice bran had greater (p<0.05) concentrations of gross energy, AEE, and copper than defatted rice bran (
Table 6). In contrast, defatted rice bran contained more (p<0.05) crude protein, ash, insoluble dietary fiber, total dietary fiber, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan, valine, alanine, glutamic acid, glycine, proline, serine, magnesium, sodium, manganese, and zinc compared with full-fat rice bran. The difference in energy concentration between full-fat and defatted rice bran is a direct result of the difference in AEE content, and the increased protein and ash concentrations in defatted rice bran is a result of concentration of these nutrients when the fat was removed.
Differences in animal responses to feeding rice bran to livestock are believed to be caused by endogenous components or physical properties such as phytate content, enzyme inhibitors, high fiber content, or oxidative rancidity, which can result in palatability reduction and gastrointestinal disturbances [
1]. As demonstrated in this study, rice bran is low in calcium and high in phosphorus, however, approximately 80% of the phosphorus in rice bran is bound to phytate. In general, rice bran contain more phytate-bound phosphorus than any other feed ingredients commonly used in diets for pigs and poultry, and phytate-bound phosphorus is largely unavailable to pigs and poultry [
24]. However, the use of microbial phytase in rice bran may release some of the phytate-bound phosphorus and improve the digestibility of phosphorus [
25].
The oil in full-fat rice bran can become rancid during storage due to the presence of a lipase that becomes active when the bran is separated from the rice kernel. Rancidity rapidly increases the free fatty acid content, which rapidly oxidizes under normal storage conditions [
26]. However, oxidation can be slowed by heating or drying after milling [
1]. The oil extracted by solvent extraction to produce defatted rice bran has a high commercial value, particularly in countries where cooking oil demand exceeds supply. Production of rice oil and defatted rice bran is, therefore, preferred by rice mills. Defatted rice bran has longer shelf life and lower mycotoxin problems than full-fat rice bran [
26]. However, it is dustier, lower in bulk density, and contains more fiber than full-fat rice bran [
27], therefore, livestock producers often prefer full-fat rice bran over defatted rice bran as an alternative ingredient due to its higher energy value [
28].
Rice bran is a valuable feed for all types of livestock and can be used to supplement oil in diets for dairy cattle [
29]. Rice bran is also used in pig and poultry diets due to its high lysine and methionine content. Inclusion of 20% full-fat or defatted rice bran in weanling pig diets had no effects on average daily gain, but inclusion of 30% of full-fat rice bran increased gain to feed ratio [
16], which is likely a result of the high AEE concentration in full-fat rice bran. In growing-finishing pigs, inclusion of 30% of full-fat rice bran improved gain to feed ratio without affecting carcass characteristics, but the addition of defatted rice bran decreased gain to feed ratio [
17] reflecting the lower energy concentration in defatted rice bran [
28]. When full-fat and defatted rice bran were fed to gestating sows, energy digestibility was greater than when fed to growing gilts, regardless of feed intake levels [
30]. In broilers diets, an inclusion level of up to 15% to 20% of full-fat or defatted rice bran may be used [
1]. Although the present study did not evaluate the effects of microbial enzymes in diets, the inclusion of microbial xylanase may increase energy utilization in rice bran, allowing for greater levels of rice bran inclusion in non-ruminant diets [
28].