Short communicationTotal dietary fiber analysis in dates and other dry fruits without starch and protein hydrolyzing enzymes
Introduction
Extensive research over the last few decades has demonstrated the vital role dietary fiber plays in gastrointestinal health and its ability to prevent or modulate symptoms associated with chronic conditions such as obesity (Bozzetto et al., 2018), type-2 diabetes (Reynolds et al., 2020) and cardiovascular diseases (Evans, 2020). Moreover, recent evidence indicates the ability of the dietary fiber to act as a prebiotic to support a healthy gut microbiome (Koç et al., 2020). Due to the multiple health benefits associated with dietary fiber consumption, there is an increasing need for dietary fiber analysis to provide adequate recommendations. Numerous analytical techniques are available for measuring TDF content in foods, including non-enzymatic gravimetric and enzymatic gravimetric methods with colorimetric or GLC/HPLC techniques. The enzymatic gravimetric method (AOAC 985.29, AOAC 991.43) is the commonly adopted analytical technique for determining TDF (Lee et al., 1992). ANKOM Technologies (Macedon, NY, USA) automated the enzymatic gravimetric method of TDF analysis. The total dietary fiber analysis method uses three enzymes, namely α-amylase, amyloglucosidase, and protease (Bolen et al., 2018). However, these enzymes are expensive, which ultimately increases the cost of analysis and limits the number of samples that can be analyzed. Li and Cardozo suggested elimination of the enzymatic hydrolysis step for samples containing <2% starch, and the method was adopted as AOAC 993.21 (Li and Cardozo, 1994). Accordingly, it may be possible to eliminate the enzyme treatment steps in the enzymatic gravimetric method.
The fruits of the date palm (Phoenix dactylifera L.) are low in starch and protein content once fully ripe (Ghnimi et al., 2017). Date fruits are typically consumed throughout the year in the Middle East, and their consumption increases exponentially in the month of Ramadan (Assaad Khalil et al., 2021). Dates are characterized by the richness in carbohydrates (60–80 %), including soluble sugars and dietary fiber (El-Sohaimy and Hafez, 2010). Date fruits are usually consumed at three developmental stages: Bisr stage (or Khalal stage), Rutab, and the fully mature Tamr stage (Amira et al., 2011). At the Bisr stage, the fruits contain about 50 % starch, which degrade during further development to the soluble sugars; glucose, fructose and sucrose (Amira et al., 2011). The main differences in the nutritional value of date fruits are mainly attributed to the components of dietary fiber, polyphenols, vitamins, and minerals (Ghnimi et al., 2017). The dietary fiber content in dates is highly variable depending on the cultivar. A study by Shahib et al. reported that the total dietary fiber in date fruits varieties range between 6.5%–11.5% (Al-Shahib and Marshall, 2003). Another study on 18 cultivars from the UAE reported a total dietary fiber content between 5.5 %–9.1 % (Habib and Ibrahim, 2011). A recent study by George et al. also showed comparable TDF content in dates (5.3–8.4 %) (George et al., 2020). Previous research indicated relatively low protein content in the Tamr stage ranging between 1.6–3.16 % (Ghnimi et al., 2017; Habib and Ibrahim, 2011). Therefore, it may be possible to eliminate the enzyme treatment steps in the ANKOM Dietary Fiber Analyzer for the enzymatic gravimetric method for TDF analysis. This study compared the total dietary fiber content values (%) in 12 date fruit varieties using the enzymatic-gravimetric method in ANKOM dietary fiber analyzer with and without enzymatic hydrolysis. The TDF content in date fruits vary considerably across different cultivars (Al‐Shahib and Marshall, 2002) and this was shown to be related to the fiber content (Kamal-Eldin et al., 2020). Thus, in our analysis we included date varieties of various textures: hard, soft and semi-hard. Moreover, we analyzed two other commonly consumed dry fruits (figs and raisins) to determine the potential application of the non-enzymatic method to other dry fruits.
Section snippets
Materials
Ten date cultivars (Barhi, Khalas, Fardh, Neghal, Reziz, Dabbas, Bouman, Shishi, Sagae, Lulu) were obtained from Al Foah Emirates Dates Company (Al-Saad, United Arab Emirates) and two cultivates from Sudan (Gundella and Barakawai). These 12 date cultivars were selected to include date fruits with soft, semi-hard, and hard textures and cover date cultivars with a wide range of fiber content. The two samples of figs and raisins were sourced from local supermarkets in Al-Ain, UAE.
Chemicals and reagents
All chemicals in
Results and discussion
The measured TDF content in the dry fruit samples analyzed is presented in Table 1. In the 12 date samples analyzed by the enzymatic method, the mean TDF content ranged from 5.4 ± 0.1 %g/100 g fruit in Barhi to 13.6 ± 0.2 %g/100 g fruit in Gundella. Similarly, the measured TDF content in dates by the non-enzymatic method ranged from 5.5 ± 0.1 %g/100 g fruit in Barhi to 12.4 ± 0.2 %g/100 g fruit in Gundella. The measured TDF content by the two methods was significantly different in 3 date
Conclusions
The results from our study conclude that the TDF analyzed using AOAC 991.43 without the enzymes gave comparable readings to the enzymatic method. This makes the non-enzymatic method an economical alternative for analyzing TDF in date fruits and other similar dry fruits such as raisins and figs. However, further studies with more sample replications are warranted to confirm the precision and accuracy of the non-enzymatic method in measuring the TDF content in dry fruits. Furthermore, studies
Funding
This project was supported by a grant from the United Arab Emirates University (grant #: G00003059).
CRediT authorship contribution statement
Habiba I. Ali: Conceptualization, Formal analysis, Investigation, Writing - original draft. Salma Alhebshi: Formal analysis, Investigation. Serene Hilary: Formal analysis, Writing - original draft. Usama Souka: Formal analysis. Fatima Al-Meqbaali: Formal analysis. Lily Stojanovska: Investigation, Writing - review & editing. Afaf Kamal Eldin: Conceptualization, Formal analysis, Investigation, Writing - review & editing.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
The authors would to thank United Arab Emirates University undergraduate students for their contribution to the preparation of the samples used in this study.
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