Dry but Not Humid Thermal Processing of Aloe vera Gel Promotes Cytotoxicity on Human Intestinal Cells HT-29

Abstract

Aloe vera products, both in food and cosmetics, are becoming increasingly popular due to their claimed beneficial effects, which are mainly attributed to the active compound acemannan. Usually, these end products are based on powdered starting materials. High temperatures during the drying process to obtain the starting materials have several advantages, like shortening the drying time, eliminating toxic aloin and reducing bacterial contamination. Nevertheless, there are two major drawbacks: first, at temperatures of 80 °C or higher, structural changes in acemannan, especially its deacetylation (>46%), are triggered, which does not happen at lower temperatures (14% at 60 °C); secondly, a toxic principle is formed at higher temperatures, resulting in a higher cytotoxicity. Thus, two temperature-dependent but opposing effects cause with a median cytotoxic concentration of CC50 = 0.4× a peak of cytotoxicity at 80 °C; at 60 °C this cytotoxic substance is not formed and at 100 °C aloin is more readily eliminated, resulting in a CC50 = 1.1× and CC50 = 1.4×, respectively. The cytotoxic substance generated by dry heat at 80 °C is not a modified polysaccharide because its polysaccharide-enriched alcohol-insoluble fraction is with CC50 = 0.9× less cytotoxic. Moreover, this substance is polar enough to be washed away with ethanol. Additionally, when Aloe gel is heated at 80 °C under humid conditions (pasteurization), the cytotoxicity does not increase (CC50 = 1.6×). Finally, to produce powdered starting materials from Aloe gel, it is recommended to use temperatures of around 60 °C in order to preserve the acemannan structure (and thus biological activity) and the low cytotoxicity.

Keywords: Aloe vera; acemannan; acetylation; cytotoxicity.

Figure 1

Polysaccharide compounds from the different Aloe vera gel samples: ILF (red), DAG60 (green), DAG80 (blue), DAG100 (cyan) (A). AILF (red), AAG60 (green), AAG80 (blue), AAG100 (cyan) (B). Error bars indicate SD. Significant differences for different samples for each compound are indicated by different letters. (The exact values can be found in Table S1 of the Supplementary Materials).

Figure 2

Monosaccharide composition of polysaccharides isolated from the different Aloe vera gel samples: ILF (red), DAG60 (green), DAG80 (blue), DAG100 (cyan) (A). AILF (red), AAG60 (green), AAG80 (blue), AAG100 (cyan) (B). Error bars indicate SD. Significant differences for different samples for each compound are indicated by different letters. (The exact values can be found in Table S2 of the Supplementary Materials).

Figure 3

Estimation of cytotoxicity by measuring metabolic activity of HT-29 after being exposed for 24 h to differently treated Aloe fillets: dehydrated DAG (A), pasteurized PAG (B), AIRs AAG (C). Samples treated at 60 °C (black square), 80 °C (red circle), 100 °C (blue diamond), ILF (green up-triangle) or ILL (cyan down-triangle). The growth control (0×) was set to 100%, the value of the positive control (20 mm H₂O₂) with 0.24 ± 0.96 is not shown. Error bars indicate SEM × 1.96.

Figure 4

Trypan blue staining of HT-29 cells exposed for 24 h with different Aloe-samples: Control (A), 1× DAG60 (B), 0.3× DAG80 (C), 1× PAG80 (D), 1× AAG80 (E), 0.3× ILF (F) and 3× AILF (G). Initial confluence was ~80% in all cases; frequently not many blue stained (dead) cells can be seen as those are washed away in a previous washing step (confluence can be evaluated). The bar indicates 50 µm.

Figure 4

Trypan blue staining of HT-29 cells exposed for 24 h with different Aloe-samples: Control (A), 1× DAG60 (B), 0.3× DAG80 (C), 1× PAG80 (D), 1× AAG80 (E), 0.3× ILF (F) and 3× AILF (G). Initial confluence was ~80% in all cases; frequently not many blue stained (dead) cells can be seen as those are washed away in a previous washing step (confluence can be evaluated). The bar indicates 50 µm.