## 3 Compositional Data on Date Seeds and Date Seed Coffee Products
### Plant Secondary Metabolites  
#### 3.4.1 Phenolic Acids and Flavonoids  
Date seeds contain a relevant amount of phenolics, primarily composed of flavonoids, which are known for their high antioxidant capacity [5]. Among the different components of the date fruit, the seeds exhibit the highest antioxidant activity, with an IC\({}_{50}\) value of approximately 24 ug/mL. Date seed coffee, which has a very strong antioxidant activity [32], is linked to its high phenolic content [26; 37]. Phenolic compounds preserve fruits against microbial and parasite infections, as well as photo-oxidation. The seeds of a plant are essential for its survival, and the high antioxidant content in the seeds may be due to their high protection value [13]. Date seeds have been found to have an inhibitory effect against Gram-positive bacteria (_Staphylococcus aureus_), but no antibacterial activity has been reported against Gram-negative bacteria (_Escherichia coli_) [54]. The phenolic content can be affected by several production-specific factors, such as the cultivar, fruit maturity, growing conditions, season, and soil type [26]. Additionally, the final measured results may be skewed by the choice of extraction conditions [37].  
The total flavonoid content is lower than the phenolic acid content. Approximately 1-2% of the total phenolic content (TPC) is flavonoids and contributes proportionally to the antioxidant activity. The _Deglet__Nour_ variety contains the highest amount of TPC (4166 mg gallic acid equivalent (GAE)/100 g d.w.) and the _Medjool_ variety contains only about half of that amount [55]. A similar result was observed when Iranian date varieties were compared. The TPC ranged from 1483 to 3377 mg GAE per 100 g d.w. Seven primary polyphenols were identified, including: cinnamic, chlorogenic, caffe, vanillic, gallic, 2.5-, and 3,5-dihydroxybenzoic acids [54]. In the _Bouhattam_ roasted date seeds, extracted with dichloromethane, three different flavonoids were present with a total concentration of 4.1 mg/100 g, including: catechin, naringenin, and apigenin. Protocatechuic and quinic acids are the major compounds in _C. arabica_ coffee beans and are also found in roasted date seeds [44]. Catechin, epicatechin, quinic acid, and protocetachuic acid are the main compounds, which are known for their high antioxidant activity. With the use of GC-MS, 13 different organic compounds were identified [44], as can be seen in Table 4.  
Procyanidin A2, B1, and B2 were detected in date seeds of the _Deglet__Nour_ cultivar using the free polyphenol fraction extraction method [56]. It has also been shown that procyanidins from date seeds undergo digestion mainly unchanged. This could result in a positive effect on the intestinal microbiome [57]. The flavonoids luteolin and quercetin are present in date seeds roasted at 160 \({}^{\circ}\)C and 180 \({}^{\circ}\)C. A higher amount was detected in the sample roasted at higher temperatures due to the increased solubilization [1]. When comparing date seeds roasted at 160 \({}^{\circ}\)C, 180 \({}^{\circ}\)C, and 200 \({}^{\circ}\)C, the TPC increases with the roasting temperature and the browning of the date seeds. The higher TPC content can be attributed to chemical reactions occurring during the roasting process, which make free phenolic compounds more readily available. The hybridizability of the tannins and gallic acid was affected by the roasting and grinding of the date seed powder [58]. The phenolic content and oxygen radical scavenging capacity (ORAC) of the tested date seed beverages are influenced by the type of coffee preparation. The sample from the espresso machine contained the highest amount of gallic acid equivalents, followed by hot water suspension,and lastly the filter brew drink (10.5 > 4.5 > 2.28 mM). The amount of coffee powder used for the espresso preparation was the lowest [59].