Best practices in heterotrophic high-cell-density microalgal processes: achievements, potential and possible limitations

Microalgae of numerous heterotrophic genera (obligate or facultative) exhibit considerable metabolic versatility and flexibility but are currently underexploited in the biotechnological manufacturing of known plant-derived compounds, novel high-value biomolecules or enriched biomass. Highly efficient production of microalgal biomass without the need for light is now feasible in inexpensive, well-defined mineral medium, typically supplemented with glucose. Cell densities of more than 100 g l−1 cell dry weight have been achieved with Chlorella, Crypthecodinium and Galdieria species while controlling the addition of organic sources of carbon and energy in fedbatch mode. The ability of microalgae to adapt their metabolism to varying culture conditions provides opportunities to modify, control and thereby maximise the formation of targeted compounds with non-recombinant microalgae. This review outlines the critical aspects of cultivation technology and current best practices in the heterotrophic high-cell-density cultivation of microalgae. The primary topics include (1) the characteristics of microalgae that make them suitable for heterotrophic cultivation, (2) the appropriate chemical composition of mineral growth media, (3) the different strategies for fedbatch cultivations and (4) the principles behind the customisation of biomass composition. The review confirms that, although fundamental knowledge is now available, the development of efficient, economically feasible large-scale bioprocesses remains an obstacle to the commercialisation of this promising technology

THE OXIDATIVE STABILITY, LIPID PROFILES AND TOTAL PHENOLICS OF ALMONDS (PRUNUS AMYGDALUS L.) AND PISTACHIOS (PISTACIA VERA L.)

Nuts contain bioactive constituents that elicit cardio-protective and anticancer effective containing phenolic compounds, healthy lipids, tocopherols, sterols and squalene. This study was undertaken to identify some bioactive constituent levels of almonds (Prunus amygdalus L.) consumed in Datça, Aegean Area, Turkey markets and pistachio (Pistacia vera L.) nuts consumed in Aegean Area, Southeastern Anatolia, Turkey markets. Total lipids, fatty acid (FAs) profiles, tocopherols, sterols and oil stability were determined on the oil extracted from the fresh nuts. Lipid content of the nuts varied between 41.2-59.8% (p<0.05) and the peroxide values (PV) of the fresh oils were 0.13-3.48 meq O2/kg oil (p<0.05). Mean monounsaturated fatty acid (MUFA) contents of almonds and pistachios were found 70.46 ± 0.67 and 62.36 ± 0.61 as % of total lipid, respectively. The major MUFA was oleic acid (C 18:1) (42.3-69.8%) while linoleic acid (C 18:2) (21.76-32.13%) was the most prevalent polyunsaturated fatty acid in almonds and pistachios. The PUFA levels ranged from 21.07-32.61 % (p<0.05). Unsaturated FAs/saturated FAs ratio was detected as 10.9 and 9.94 for almonds and pistachios, respectively. The major tocopherol was alfa-tocopherol in almonds (36.8 ± 4.7 mg/100 g oil) whereas gamma tocopherol level was major in pistachios (37.3 ± 3.4 mg/100 g oil) (p<0.05). The major sterol was identified as beta-sitosterol and its content was avg. 2155.2 ± 11.3 mg/g oil in almonds while that of content was 4706.5 ± 73.2 mg/g oil in pistachios (p<0.05). Total phenolics (TPs) of almonds with skin, TPs of almonds without skin and TPs of pistachios were avg. 313.6 ± 1.28; avg. 57.44 ± 1.1; avg. 922.6 ± 2.8 as mg of gallic acid equivalent (GAE)/100 g, respectively. All data obtained from almond and pistachios was evaluated by multivariate analysis using SPSS (ver.13.0) statistical package program. Almond and pistachios were differantiated with good separation based on the functional lipids, lipid constituents and total phenolic contents via Principal Component Analysis (PCA). In this context, almonds and pistachios can be consumed as good energy snacks in daily nutrition and the multivariate techniques can differentiate these nuts based on their oxidative stability, lipid profiles and total phenolics